ukssdc_i.bib

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@COMMENT{{{Command line: /soft/ukssdc/share/bib2bib -c 'exists ukssdc_i' -s author -ob ukssdc_i.bib ukssdc.bib}}

@ARTICLE{altadill2003:_time_scale,
  AUTHOR = {Altadill, D. and Apostolov, E.M.},
  TITLE = {Time and scale size of planetary wave signatures in the
                  ionospheric F region: Role of the geomagnetic activity and
                  mesosphere/lower thermosphere winds},
  JOURNAL = {Journal of Geophysical Research},
  YEAR = {2003},
  VOLUME = {108},
  NUMBER = {A11},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1029/2003JA010015},
  ABSTRACT = {The time and scale size of planetary wave signatures (PWS)
                  in the mid latitude F region ionosphere of the Northern
                  Hemisphere and the main pattern of their possible sources of
                  origin are presented. The PWS involved in this study have
                  periods of about 2-3, 5-6, 10, 13.5, and 16 days. The PWS in
                  the ionosphere are large scale phenomena. PWS with periods
                  of about 2-3 and 5-6 days have a typical longitudinal size
                  of 80degrees, they are coherent some 6000 km apart, and they
                  occur about 12% and 14% of the entire observational record
                  respectively. The typical longitudinal size of PWS with
                  periods of about 10 and 13 days is 100degrees, they are
                  coherent some 7500 km apart, and they occur about 24% and
                  22% of the entire observational record respectively. PWS
                  with periods of about 16 days seem to be global scale
                  phenomena, and they occur about 30% of the entire
                  observational record. The results estimate that geomagnetic
                  activity variations play the most important role for driving
                  PWS in the ionosphere. The geomagnetic activity variations
                  can drive at least 20-30% of the PWS with periods of about
                  2-3, 5-6, 10 and 16 days, but even up to 65-70% for the PWS
                  with periods of about 10 and 16 days, and they practically
                  drive 100% of the PWS with periods of about 13.5 days. The
                  planetary wave activity in the mesosphere/lower thermosphere
                  (MLT) winds can drive about 20-30% of the PWS with periods
                  of about 2-3, 5-6, 10 and 16 days. There is a significant
                  percentage of existence of PWS in the F region apparently
                  'independent' from the geomagnetic activity variations and
                  of the MLT winds. The latter is better expressed for PWS
                  with shorter period. PWS with periods of about 13.5 days are
                  an exception to that. A candidate mechanism for the
                  'independent' events may be the non linear interaction or
                  the amplitude modulation between different PWS.}
}

@ARTICLE{altadill2003,
  AUTHOR = {Altadill, D. and Apostolov, E.M. and Jacobi, C. and
                  Mitchell, N.J.},
  TITLE = {Six-day westward propagating wave in the maximum electron
                  density of the ionosphere},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2003},
  VOLUME = {21},
  NUMBER = {7},
  PAGES = {1577--1588},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {},
  ABSTRACT = {Analyses of time-spatial variations of critical plasma
                  frequency foF2 during the summer of 1998 reveal the
                  existence of an oscillation activity with attributes of a
                  6-day westward propagating wave. This event manifests itself
                  as a global scale wave in the foF2 of the Northern
                  Hemisphere, having a zonal wave number 2. This event
                  coincides with a 6-day oscillation activity in the
                  meridional neutral winds of the mesosphere/lower
                  thermosphere (MLT). The oscillation in neutral winds seems
                  to be linked to the 6-7-day global scale unstable mode
                  westward propagating wave number I in the MLT. The forcing
                  mechanisms of the 6-day wave event in the ionosphere from
                  the wave activity in the MLT are discussed.}
}

@ARTICLE{altadill2001,
  AUTHOR = {Altadill, D. and Gauthier, F. and Vila, P. and Sole,
                  J.G. and Miro, G. and Berranger, R.},
  TITLE = {The 11.08.1999 solar eclipse and the ionosphere: a search
                  for the distant bow-wave},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2001},
  VOLUME = {63},
  NUMBER = {9},
  PAGES = {925--930},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {The advantage of studying eclipse disturbances is the
                  perfect predictability of their 4D source geometry, which
                  allows for preparation of adapted systems and schedules. The
                  total solar eclipse period of August 11, 1999 across Europe
                  was notable for exceptionally uniform solar disk, steady
                  solar wind and quiet magnetospheric conditions. Large-scale
                  gravity wave activity prior to the eclipse however disturbed
                  the initial 0900 LT thermosphere weather. This rapid letter
                  is an advance summary about one particular aspect of the
                  West European ionosonde and radar results of the eclipse
                  experiment. It focusses on the possible emergence of a
                  distant eclipse frontal bow-wave. This was expected as a
                  consequence of the supersonic shock of stratospheric Ozone
                  cooling. First-look data of Vertical Incidence Digisonde
                  records are greatly improved by their Real-Time acquisition
                  of inverted true-height profiles. The EBRE (Tortosa, Spain)
                  foF1 and foF2 simultaneous oscillations observed from the
                  second to the fourth hour following maximum solar
                  occultation appear as convincing indicators of the bow-wave
                  signature. Large fluctuations in foF1 and foF2 during some
                  of our control days, of usual gravity wave character,
                  emphasize the importance of meteorologic disturbances on
                  mid-latitude ionosphere variability.}
}

@ARTICLE{altinay97:_forec,
  AUTHOR = {Altinay, O. and Tulunay, E. and Tulunay, Y.K.},
  TITLE = {Forecasting of ionospheric critical frequency using neural
                  networks},
  JOURNAL = {Geophysical Research Letters},
  PAGES = {1467--1470},
  YEAR = {1997},
  MONTH = JUN,
  VOLUME = {24},
  NUMBER = {12},
  ABSTRACT = {Multilayer perceptron type neural networks (NN) are employed
                  for forecasting ionospheric critical frequency (foF2) one
                  hour in advance. The nonlinear black-box modeling approach
                  in system identification is used. The main contributions:
                  1. A flexible and easily accessible training database
                  capable of handling extensive physical data is prepared,
                  2. Novel NN design and experimentation software is
                  developed, 3. A training strategy is adopted in order to
                  significantly enhance the generalization or extrapolation
                  ability of NNs, 4. A method is developed for determining the
                  relative significances (RS) of NN inputs in terms of mapping
                  capability.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{araujo-pradere01:_evaluat_storm_time_ionos_empir,
  AUTHOR = {Araujo-Pradere, E.A. and Fuller-Rowell, T.J.},
  TITLE = {Evaluation of the STORM Time Ionospheric Empirical Model for
                  the Bastille Day event},
  JOURNAL = {Solar Physics},
  PAGES = {317--324},
  YEAR = {2001},
  MONTH = {Dec},
  VOLUME = {204},
  NUMBER = {1-2},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {Recent theoretical model simulations of the ionosphere
                  response to geomagnetic storms have provided the
                  understanding for the development of an emperical storm-time
                  ionospheric model (STORM). The emperical model is driven by
                  the previous time-history of a_p, and is designed to scale
                  the quiet-time F-layer critical frequency (f_oF_2) to
                  account for storm-time changes in the ionosphere. The model
                  provides a useful, yet simple tool for modeling of the
                  perturbed ionosphere. The quality of the model prediction
                  has been evaluated by comparing with the observed
                  ionospheric response during the Bastille Day (July
                  2000)storm. With a maximum negative D_st of -290 nT and an
                  a_p of 400, this magnetic perturbation was the strongest of
                  year 2000. For these conditions, the model output was
                  compared with the actual ionospheric response from all
                  available stations, providing a reasonable latitudinal and
                  longitudinal coverage. The comparisons show that the model
                  captures the decreases in electron density particularly well
                  in the northern summer hemisphere. In winter, the observed
                  ionospheric response was more variable, showing a less
                  consistent response, imposing a more severe challenge to the
                  emperical model. The value of the model has been quantified
                  by comparing the root mean square error (RMSE) of the STORM
                  predictions with the monthly mean. The results of this study
                  illustrate that the STORM model reduces the RSME at the peak
                  of the disturbance from 0.36 to 0.22, a significant
                  improvement over climatology.}
}

@ARTICLE{araujo-pradere02:_storm2,
  AUTHOR = {Araujo-Pradere, E.A. and Fuller-Rowell, T.J. and 
                  Codrescu, M.V.},
  TITLE = {STORM: An empirical storm-time ionospheric correction model
                  - 2. Validation},
  JOURNAL = {Radio Science},
  YEAR = {2002},
  MONTH = {Sept},
  VOLUME = {37},
  NUMBER = {5},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1029/2002RS002620},
  ABSTRACT = {[1] STORM is an empirical ionospheric correction model
                  designed to capture the changes in F region electron density
                  during geomagnetic storms. The model is driven by the
                  previous 33 hours of a(p), and the output is used to scale
                  the quiet time F region critical frequency (foF2) to account
                  for increases or decreases in electron density resulting
                  from a storm. The model provides a simple tool for modeling
                  the perturbed ionosphere. The quality of the model has been
                  evaluated by comparing the predictions of the model with the
                  observed ionospheric response during the six storms in the
                  year 2000. The model output has been compared with the
                  actual ionospheric response at 15 ionosonde stations for
                  each storm. The comparisons show that the model captures the
                  decreases in electron density particularly well in summer
                  and equinox at midlatitudes and high latitudes but is less
                  accurate in winter. The value of the model has been
                  quantified by comparing the daily root mean square error of
                  the STORM predictions with the monthly mean. The results of
                  the validation show that there is a 33% improvement of the
                  STORM model predictions over the monthly median during the
                  storm days and that the model captures more than half of the
                  increase in variability on the storm days, a significant
                  advance over climatology.}
}

@ARTICLE{araujo-pradere2003,
  AUTHOR = {Araujo-Pradere, E.A. and Fuller-Rowell, T.J. and Bilitza,
                  D.},
  TITLE = {Validation of the STORM response in IRI2000},
  JOURNAL = {Journal of Geophysical Research},
  YEAR = {2003},
  VOLUME = {108},
  NUMBER = {A3},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1029/2002JA009720},
  ABSTRACT = {[1] The latest version of the International reference
                  ionosphere, IRI2000 [Bilitza, 2001], contains a dependence
                  on geomagnetic activity based on an empirical storm-time
                  ionospheric correction model (STORM) [Araujo-Pradere et al.,
                  2002]. The new storm correction in IRI is driven by the
                  previous time history (33 hours) of ap and is designed to
                  scale the normal quiet-time F layer critical frequency
                  (f(o)F(2)) to account for storm-time changes in the
                  ionosphere. An extensive validation of IRI2000 has been
                  performed during geomagnetic storm conditions to determine
                  the validity of the new algorithms. The quality of the
                  storm-time correction has been evaluated by comparing the
                  model with the observed ionospheric response during all the
                  geomagnetic storms with ap > 150 in 2000 and 2001, a total
                  of 14 intervals. The model output was compared with the
                  actual ionospheric response for all available ionosonde
                  stations for each storm. The comparisons show that the model
                  captures the decreases in electron density particularly well
                  in summer and equinox conditions. To quantify the
                  improvement in IRI2000, the root-mean-square error has been
                  evaluated and compared with the previous version of IRI,
                  which had no geomagnetic dependence. The results indicate
                  that IRI2000 has almost a 30% improvement over IRI95 during
                  the storm days and is able to capture more than 50% of the
                  increase in variability, above quiet times, due to the
                  storms.}
}

@ARTICLE{araujo-pradere2005,
  AUTHOR = {Araujo-Pradere, E.A. and Fuller-Rowell, T.J. and Bilitza,
                  D.},
  TITLE = {Time Empirical Ionospheric Correction Model (STORM) response
                  in IRI2000 and challenges for empirical modeling in the
                  future},
  JOURNAL = {Radio Science},
  YEAR = {2004},
  VOLUME = {39},
  NUMBER = {1},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1029/2002RS002805},
  ABSTRACT = {IRI2000 [Bilitza, 2001] now contains a geomagnetic activity
                  dependence based on the Time Empirical Ionospheric
                  Correction Model (STORM) [Araujo-Pradere and Fuller-Rowell,
                  2002; Araujo-Pradere et al., 2002]. The storm correction is
                  driven by the previous time history of a(p) and is designed
                  to scale the quiet time F layer critical frequency
                  (f(o)F(2)) to account for storm-time changes in the
                  ionosphere. The quality of the storm-time correction was
                  recently evaluated by comparing the model with the observed
                  ionospheric response during all the significant geomagnetic
                  storms in 2000 and 2001. The model output was compared with
                  the actual ionospheric response at 15 stations for each
                  storm. These quantitative comparisons using statistical
                  metrics showed that the model captures the decreases in
                  electron density particularly well in summer and equinox
                  conditions, but is not so good during winter conditions. To
                  further assess the capabilities of the model, STORM has been
                  compared in detail with observations during the Bastille Day
                  storm in July 2000. This storm, considered to be on the
                  extreme end of the statistical scale of storm magnitude,
                  highlights two main areas were challenges remain for the
                  empirical storm-time ionospheric model. The first is the
                  rapid onset of the positive storm phase; the second is the
                  regional composition changes that can affect one longitude
                  sector at the expense of another for a particular
                  storm. Both these challenges, although appreciated during
                  the development of STORM, remain to be addressed.}
}

@ARTICLE{araujo-pradere02:_storm1,
  AUTHOR = {Araujo-Pradere, E.A. and Fuller-Rowell, T.J. and Codrescu,
                  M.V.},
  TITLE = {STORM: An empirical storm-time ionospheric correction model
                  - 1. Model description},
  JOURNAL = {Radio Science},
  YEAR = {2002},
  MONTH = {Sept},
  VOLUME = {37},
  NUMBER = {5},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1029/2001RS002467},
  ABSTRACT = {Using data from 75 ionosonde stations and 43 storms, and
                  based on the knowledge gained from simulations from a
                  physically based model, we have developed an emperical
                  ionospheric storm-time correction model. The model is
                  designed to scale the quiettime F region critical frequency
                  (foF2) to account for storm-time changes in the
                  ionosphere. The model is driven by a new index based on the
                  integral of the a_p index over the previous 33 hours
                  weighted by a filter obtained by the method of singular
                  value decomposition. Ionospheric data was stored as a
                  function of season and latitude and by intensity of of the
                  storm, to obtain the corresponding dependencies. The good
                  fit to data at midlatitudes for storms during summer and
                  equinox enable a reliable correction, but during winter and
                  near the equator, the model does not improve significantly
                  on the quiet time International Reference Ionosphere
                  predictions. This model is now included in the international
                  recommended standard IRI2000[Bilitza 2001] as a correction
                  factor for perturbed conditions.}
}

@ARTICLE{araujo-pradere2005:_variability,
  AUTHOR = {Araujo-Pradere, E.A. and Fuller-Rowell, T.J. and Codrescu, 
                  M.V.},
  TITLE = {Characteristics of the ionospheric variability as a function 
                  of season, latitude, local time, and geomagnetic activity},
  JOURNAL = {Radio Science},
  YEAR = {2005},
  VOLUME = {40},
  NUMBER = {5},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1029/2004RS003179},
  ABSTRACT = {An
	ionospheric F-2 critical frequency database has been  assembled to
	  determine the variability of the F region as a function of local
	    time, latitude, season, and geomagnetic activity. The database
	comprises observations from 75 ionosonde stations covering a range
	      of geomagnetic latitude and includes 43 storm intervals. The
	  database was previously used to develop the Storm-Time Empirical
	       Ionospheric Correction Model (STORM). The mean and standard
	  deviation have been evaluated by sorting the data by local time,
		 season (five intervals centered on equinox, solstice, and
      intermediate intervals), latitude (four regions each 20 degrees wide
	   in geomagnetic latitude), and up to eight levels of geomagnetic
	  activity. The geomagnetic activity index was based on a weighted
      integral of the previous 33 hours of ap and is the same as that used
	   by the STORM model. The database covers a full solar cycle, but
	  insufficient information was available to sort by solar activity
	    without compromising the estimates of variability on the other
       sorting parameters. About half the data were contained in the first
	level of geomagnetic activity, between 0 and 500 units of filtered
	ap corresponding to Kp <= 2, and half above that level. When local
	 time dependence was included in the binning, sufficient data were
      available to sort into two levels of geomagnetic activity, quiet (Kp
       <= 2(+)) and disturbed (Kp > 3(-)). For all latitudes and levels of
       geomagnetic activity, the lowest variability was typically found in
	   summer (10-15%), and the largest variability occurred in winter
		(15-40%), with equinox (10-30%) lying between the solstice
	   extremes. The exception was low latitudes at equinox, which had
	    surprising low variability (10%), possibly because of the weak
	     interhemispheric flow at this time of year. At middle and low
	    latitudes, the variability tended to increase with geomagnetic
	    activity in winter and equinox but remained fairly constant in
	  summer. At high latitudes, the surprising result was that in all
	   seasons, and in winter in particular, the variability tended to
	  decrease, probably because of the increased upwelling of neutral
		    molecular species and stronger chemical control of the
	      ionosphere. The data have also been used to build a table of
	 estimated variability suitable for inclusion in the International
       Reference Ionosphere or any other climatological model. For periods
       where data were scarce or nonexistent, an estimated variability was
	      provided on the basis of expectations of the consequences o
	     physical processes. This was necessary to fill in the table o
	  values in order to develop a module suitable for inclusion in th
				    International Reference Ionosphere.}
}

@ARTICLE{austin:_whatever_happened_to_40_metres,
  AUTHOR = {Austin, B.A.},
  TITLE = {Whatever Happened to 40 Metres?},
  JOURNAL = {Mercury, the Journal of the Royal Signals Amateur Radio
                  Society},
  YEAR = {2005},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}

@ARTICLE{bamford2001,
  AUTHOR = {Bamford, R.A.},
  TITLE = {The effect of the 1999 total solar eclipse on the
                  ionosphere},
  JOURNAL = {Physics and Chemistry of the Earth - C},
  YEAR = {2001},
  VOLUME = {26},
  NUMBER = {5},
  PAGES = {373--377},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  ABSTRACT = {The localised "night" created as the moon's shadow travelled
                  across the Earth during the total solar eclipse of 11th
                  August 1999, produced changes in the ionosphere across
                  Europe that were monitored with a variety of modern
                  instrumentation. The passage of the 100km wide, super-sonic
                  lunar shadow offered the opportunity to examine the changes
                  in electron densities, radio absorption, neutral wind
                  patterns and the possible generation of waves in the layers
                  of the ionosphere. All these for an event for which the
                  cause of the disturbance can be calculated with
                  accuracy. Reported here are the results from the vertical
                  ionosondes located under the path of totality and in the
                  partial eclipse region and dual frequency GPS TEC
                  measurements. The ionosondes showed that even in the partial
                  shadow the peak electron densities of the F & E ionospheric
                  layers decreased by as much as 20-35\%. The TEC measurements
                  showed that the vertical equivalent line integrated electron
                  density dropped by 15\% at the 97\% partial eclipse north of
                  the path of totality. The consequences of these observations
                  are discussed in relation to making model predictions.}
}

@ARTICLE{belahaki2005,
  AUTHOR = {Belehaki, A. and Cander, Lj. and Zolesi, B. and Bremer, J. and Juren, C. and Stanislawska, I. and Dialetis, D. and Hatzopoulos, M.},
  TITLE = {DIAS Project: The establishment of a European digital upper 
                  atmosphere server},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2005},
  VOLUME = {67},
  NUMBER = {12},
  PAGES = {1092--1099},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {},
  ABSTRACT = {The main objective of DIAS (European Digital Upper Atmosphere Server) project is to develop a pan-European digital data collection on the state of the upper atmosphere, based on real-time information and historical data collections provided by most operating ionospheric stations in Europe. A DIAS system will distribute information required by various groups of users for the specification of upper atmospheric conditions over Europe suitable for nowcasting and forecasting purposes. The successful operation of the DIAS system will lead to the development of new European added-value products and services, to the effective use of observational data in operational applications and consequently to the expansion of the relevant European market.},
  KEYWORDS = {Ionosphere; Upper atmosphere; Ionospheric monitoring; Ionospheric nowcasting; Ionospheric forecasting; Digital libraries},
  URL = {http://dx.doi.org/10.1016/j.jastp.2005.02.021}
}

@ARTICLE{belehaki02,
  AUTHOR = {Belehaki, A. and Tsagouri, I.},
  TITLE = {On the occurrence of storm-induced nighttime ionization
                  enhancements at ionospheric middle latitudes},
  JOURNAL = {Journal of Geophysical Research},
  PAGES = {1209},
  YEAR = {2002},
  VOLUME = {107},
  NUMBER = {A8},
  ABSTRACT = {Ionospheric observations from nine middle-latitude stations
                  are studied for five magnetic storms that occurred during
                  September and October 2000. The correlation between various
                  solar wind, magnetospheric and ionospheric parameters shows
                  that the nighttime ionospheric response is strongly
                  dependent on the conditions during which solar
                  wind-magnetosphere coupling occurred. Storms with initial
                  compressive phase and rapidly evolving main phase have as a
                  global effect the ionization depletion in the nightside at
                  middle latitudes, independent of the storm intensity. These
                  storms are caused by the abrupt dissipation of a large
                  amount of energy input, resulting in the rapid expansion of
                  the neutral composition disturbance zone equatorward,
                  producing the observed negative effects in all middle
                  latitude stations presented here. Gradually evolving
                  geomagnetic storms, driven by slowing increasing southward
                  IMF, result in the observation of positive effects at night
                  in low to middle latitude stations. The weaker the intensity
                  of the storm is, according to the Dst index, the more likely
                  it is that one will observe nighttime ionization
                  enhancements in subauroral latitudes as well. There are two
                  competing mechanisms causing the observed effects; the
                  expansion of the neutral composition disturbance zone
                  results in negative effects, while downward plasmaspheric
                  fluxes produce ionization enhancements at night. Gradually
                  evolving storms are characterized by the restricted
                  development of the neutral composition disturbance zone to
                  higher latitudes, and the extent of its equatorward boundary
                  depends on the intensity of the storm. During storms of this
                  type, the role of plasmaspheric fluxes dominates at middle
                  to low latitudes. Their effects are observable up to
                  subauroral latitudes given that the neutral composition
                  disturbance zone development is restricted to higher
                  latitudes, as happens when the geomagnetic activity is of
                  low or moderate intensity.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{bencze05,
  AUTHOR = {Bencze, P.},
  TITLE = {On the long-term change of ionospheric parameters},
  JOURNAL = {jastp},
  YEAR = 2005,
  VOLUME = 67,
  NUMBER = 14,
  PAGES = {1298--1306},
  MONTH = {September},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1016/j.jastp.2005.06.020},
  ABSTRACT = {Independent of the possible sources (solar activity, geomagnetic activity, greenhouse effect, etc.) of a global change in the upper atmosphere, it is the sign of a long-term trend of temperature that might reveal the cause of a global change.

Long-term change of temperature in the F region of the ionosphere has been studied and is assumed to be expressed in terms of thickness of the bottornside F2 layer characterized by the difference between height of the maximum electron density of the F2 layer hmF2 and altitude of the lower boundary of the F region represented by h'F. Using the difference of two ionospheric parameters has the advantage that it reduces the effect of changes resulting from alteration of equipment and scaling personnel. In this study, in summer only night values of the difference hmF2-h'F and in winter both day and night values have been taken into account considering that h'F might indicate the lower boundary of the F region in these periods. The study of the behaviour of hmF2-h'F taking separately the stations and determining yearly the mean measure (trend) of the variation of hmF2-h'F with solar and geomagnetic activities found that this difference increases significantly with enhanced solar activity, but trends of the solar activity effect exerted on this difference themselves do not practically change with increasing sunspot number. Further, hmF2-h'F decreases only insignificantly with growing geomagnetic activity. Trends of the geomagnetic activity effect related to hmF2-h'F change only insignificantly with increasing Ap; however, trends of the geomagnetic activity effect decreased with increasing latitude.

As a result of this investigation it has been found that hmF2-h'F regarded as thickness of the bottornside F2 layer shows an effect of the change of solar activity during the last three solar cycles, indicating temperature change in the upper atmosphere to be expected on the basis of changing solar activity. Furthermore, though a long-term variation of solar activity considering only years around solar activity minima is relatively small, the difference hmF2-h'F indicates a trend opposing the change of solar activity; that is, it decreases slightly during the first three 20, 21, 22 solar cycle minima (1964-1986), but decreases more abruptly according to the change of solar activity towards the minimum of solar cycle 23 (1986-1996), thus also indicating variation of temperature in the F region. However, this variation cannot be explained by the change of solar and geomagnetic activities alone, but assumes some other source (e.g. greenhouse gases) too. (c) 2005 Elsevier Ltd. All rights reserved.}
}

@ARTICLE{bessarab2002,
  AUTHOR = {Bessarab, F.S. and Korenkov, Y.N. and Klimenko, V.V. and
                  Natsvalyan, N.S.},
  TITLE = {Modeling the thermospheric and ionospheric response to the
                  solar eclipse of August 11, 1999},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2002},
  VOLUME = {42},
  NUMBER = {5},
  PAGES = {644--651},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {The results of model computations of thermospheric and
                  ionospheric effects of the solar eclipse of August 11, 1999,
                  are reported. The computations are performed in terms of a
                  self-consistent global model of the Earth's thermosphere,
                  ionosphere, and protonosphere. It is shown that during the
                  eclipse, the neutral gas temperature in the thermosphere
                  decreases by 90 K, absolute concentrations of O and N-2
                  components decrease by 20 and 40%, respectively, and the
                  wind regime changes so that it allows the amplitude of
                  neutral gas velocity to change by 100 m/s. The results of
                  foF2 computations are compared to the experimental data
                  obtained at Chilton station (51.3degreesN, 1degreesW) during
                  the eclipse of August 11, 1999. The decrease in foF2 reaches
                  similar to1 MHz. It is shown that some of the thermospheric
                  and ionospheric parameters do not rapidly recover after the
                  eclipse. In particular, T-n and the concentration of N-2
                  remained low above Chilton station until the end of the
                  day. The diurnal variation in foF2 increases at 1800 UT
                  compared to undisturbed conditions.}
}

@ARTICLE{bilge00,
  AUTHOR = {Bilge, A.H. and Tulunay, Y.K.},
  TITLE = {A novel on-line for single station prediction and
                  forecasting of the ionospheric critical frequency foF2 1
                  hour ahead},
  JOURNAL = {Geophysical Research Letters},
  PAGES = {1383--1386},
  YEAR = {2000},
  MONTH = {may},
  VOLUME = {27},
  NUMBER = {9},
  ABSTRACT = {The unpredictable variability of the ionospheric F region
                  greatly limits the efficiency of communications, radar and
                  navigation systems which employ high frequency (HF)
                  radiowaves. The objective of this work is to forecast the
                  ionospheric critical frequency values (foF2) one hour in
                  advance. For this a novel method has been developed for
                  1-hour ahead forecasting of the critical frequency of the F2
                  layer (foF2) based on applying feedback on predicted monthly
                  median values of foF2 for each hour. The basic model for the
                  prediction of the monthly medians consists of a parabolic
                  dependency on R12 superimposed by a trigonometric expansion
                  in terms of the harmonics of yearly variation, linearly
                  modulated by R12. The monthly medians for each hour are
                  predicted by applying the basic model over a sliding data
                  window.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{blanch2005,
  AUTHOR = {Blanch, E. and Altadill, D. and Boska, J. and Buresova, D. 
                  and Hernandez-Pajares, M.},
  TITLE = {November 2003 event: Effects on the Earth's ionosphere 
                  observed from ground-based ionosonde and GPS data},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2005},
  VOLUME = {23},
  NUMBER = {9},
  PAGES = {3027--3034},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://overview.sref.org/1432-0576/ag/2005-23-3027},
  ABSTRACT = {Intense late-cycle solar activity during October and November
                  2003 produced two strong geomagnetic storms: 28 October-5 
                  November 2003 (October) and 1923 November 2003 (November); 
                  both reached intense geomagnetic activity levels, K-p = 9, 
                  and K-p = 8+, respectively. The October 2003 geomagnetic 
                  storm was stronger, but the effects on the Earth's ionosphere
                  in the mid-latitude European sector were more important 
                  during the November 2003 storm. The aim of this paper is to 
                  discuss two significant effects observed on the ionosphere 
                  over the mid-latitude European sector produced by the 
                  November 2003 geomagnetic storm, using, data from ground 
                  ionosonde at Chilton (51.5 degrees N; 359.4 degrees E), 
                  Pruhonice (50.0 degrees N; 14.6 degrees E) and El Arenosillo 
                  (37.1 degrees N; 353.3 degrees E), jointly with GPS data. 
                  These effects are the presence of well developed anomalous 
                  storm E, layers observed at latitudes as low as 37 degrees N 
                  and the presence of two thin belts: one having enhanced 
                  electron content and other, depressed electron content. Both 
                  reside over the mid-latitude European evening sector.}
}

@UNPUBLISHED{bradley1993,
  AUTHOR = {Bradley, P.A.},
  TITLE = {A study of the differences in foF2 and M(3000)F2 between
                  solar cycles},
  YEAR = {1993},
  NOTE = {Given at URSI GA 1993},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}

@ARTICLE{bradley98:_instan_europ_hf,
  AUTHOR = {Bradley, P.A. and Juchnikowski, G. and Rothkaehl, H. and
                  Stanislawska, I.},
  TITLE = {Instantaneous maps of the European middle and high-latitude
                  ionosphere for HF propagation assessments},
  JOURNAL = {Advances in Space Research},
  PAGES = {861--864},
  YEAR = {1998},
  MONTH = OCT,
  VOLUME = {22},
  NUMBER = {6},
  ABSTRACT = {Instantaneous mapping techniques applied to geographically
                  irregularly spaced foF2 measurements can lead sometimes to
                  non-physical gradients. A procedure is presented to avoid
                  such problems by the use of screen points within the area of
                  interest having values derived from single station models
                  (SSM's). Spatial smoothing uses the kriging method in terms
                  of the deviations between the measurements and corresponding
                  figures given by the adopted long-term mapping method of
                  COST 238 (PRIME). A new first-order trough model is
                  introduced as a correction to the mapped values on the
                  equatorial side of the auroral oval by night. Sample maps of
                  the European ionosphere generated by this technique are
                  compared with internationally recommended monthly median
                  prediction maps to demonstrate the lack of spatial structure
                  these latter give, with consequential errors when applied to
                  propagation assessments. The use of the new maps,
                  particularly for the higher latitudes, is advocated.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}

@ARTICLE{bremer04:trends_ionosphere,
  AUTHOR = {Bremer, J.},
  TITLE = {Investigations of long-term trends in the ionosphere with
                  world-wide ionosonde observations},
  JOURNAL = {Advances in Space Research},
  YEAR = {2004},
  VOLUME = 2,
  PAGES = {253--258},
  ABSTRACT = {Basing on model calculations by Roble and Dickinson (1989)
                  for an increasing content of atmospheric greenhouse gases in
                  the Earth's atmosphere Rishbeth (1990) predicted a lowering
                  of the ionospheric F2- and E-regions. Later Rishbeth and
                  Roble (1992) also predicted characteristic longterm changes
                  of the maximum electron density values of the ionospheric
                  E-, F1-, and F2-layers. Long-term observations at more than
                  100 ionosonde stations have been analyzed to test these
                  model predictions. In the E- and F1-layers the derived
                  experimental results agree reasonably with the model trends
                  (lowering of h0E and increase of foE and foF1, in the
                  E-layer the experimental values are however markedly
                  stronger than the model data). In the ionospheric F2-region
                  the variability of the trends derived at the different
                  individual stations for hmF2 as well as foF2 values is too
                  large to estimate reasonable global mean trends. The reason
                  of the large differences between the individual trends is
                  not quite clear. Strong dynamical effects may play an
                  important role in the F2-region. But also inhomogeneous data
                  series due to technical changes as well as changes in the
                  evaluation algorithms used during the long observation
                  periods may influence the trend analyses.},
  URL = {http://www.copernicus.org/URSI/ars/ARS_2_1/253.pdf},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{bremer98:_trend_e_f_europ,
  AUTHOR = {Bremer, J.},
  TITLE = {Trends in the ionospheric E and F regions over Europe},
  JOURNAL = {Annales Geophysicae},
  PAGES = {986--996},
  YEAR = {1998},
  VOLUME = {16},
  NUMBER = {8},
  ABSTRACT = {Continuous observations in the ionospheric E and F regions
                  have been regularly carried out since the fifties of this
                  century at many ionosonde stations. Using these data from 31
                  European stations long-term trends have been derived for
                  different parameters of the ionospheric E layer (h' E, foE),
                  F1 layer (foF1) and F2 layer (hmF2, foF2). The detected
                  trends in the E and F1 layers (lowering of the E region
                  height h'E; increase of the peak electron densities of the E
                  and F1 layers, foE and foF1) are in qualitative agreement
                  with model predictions of an increasing atmospheric
                  greenhouse effect. In the F2 region, however, the results
                  are more complex. Whereas in the European region west of
                  30 E negative trends in hmF2 (peak height of the F2
                  layer) and in the peak electron density (foF2) have been
                  found, in the eastern part of Europe (east of 30 E)
                  positive trends dominate in both parameters. These marked
                  longitudinal differences cannot be explained by an
                  increasing greenhouse effect only, here probably dynamical
                  effects in the F2 layer seem to play an essential role.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{bremer04:_long_term,
  AUTHOR = {Bremer, J. and Alfonsi, L. and Bencze, P. and Lastovicka,
                  J. and Mikhailov, A.V. and Rogers, N.},
  TITLE = {Long-term trends in the ionosphere and upper atmosphere
                  parameters},
  JOURNAL = {Annals of Geophysics},
  PAGES = {1009--1029},
  YEAR = {2004},
  VOLUME = {47},
  NUMBER = {2--3},
  ABSTRACT = {The first part of the paper is directed to the investigation
                  of the practical importance of possible longterm trends in
                  the F2-layer for ionospheric prediction models. Using
                  observations of about 50 different ionosonde stations with
                  more than 30 years data series of foF2 and hmF2, trends have
                  been derived with the solar sunspot number R-12 as index of
                  the solar activity. The final result of this trend analysis
                  is that the differences between the trends derived from the
                  data of the individual stations are relatively large, the
                  calculated global mean values of the foF2 and hmF2 trends,
                  however, are relatively small. Therefore, these small global
                  trends can be neglected for practical purposes and must not
                  be considered in ionospheric prediction models. This
                  conclusion is in agreement with the results of other
                  investigations analyzing data of globally distributed
                  stations. As shown with the data of the ionosonde station
                  Tromso, however, at individual stations the ionospheric
                  trends may be markedly stronger and lead to essential
                  effects in ionospheric radio propagation. The second part of
                  the paper deals with the reasons for possible trends in the
                  Earth's atmo- and ionosphere as investigated by different
                  methods using characteristic parameters of the ionospheric
                  D-, E-, and F-regions. Mainly in the F2-region different
                  analyses have been carried out. The derived trends are
                  mainly discussed in connection with an increasing greenhouse
                  effect or by long-term changes in geomagnetic activity. In
                  the F I-layer the derived mean global trend in foF1 is in
                  good agreement with model predictions of an increasing
                  greenhouse effect. In the E-region the derived trends in foE
                  and h'E are compared with model results of an atmospheric
                  greenhouse effect, or explained by geomagnetic effects or
                  other anthropogenic disturbances. The trend results in the
                  D-region derived from ionospheric reflection height and
                  absorption measurements in the LF, MF and HF ranges can at
                  least partly be explained by an increasing atmospheric
                  greenhouse effect.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {}
}

@ARTICLE{buresova2000,
  AUTHOR = {Buresova, D. and Lastovicka, J.},
  TITLE = {Hysteresis of foF2 at European middle latitudes},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2000},
  VOLUME = {18},
  NUMBER = {8},
  PAGES = {987--991},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {The hysteresis of foF2 is studied for several European
                  stations over the whole 24-hour diurnal interval for the
                  equinoctial months of the years just before and just after
                  the solar cycle minimum for solar cycles 20 and 21. Based on
                  previous results, the hysteresis is expected to develop best
                  just for the equinoctial months and near the solar cycle
                  minimum. The hysteresis is generally found to be negative,
                  i.e. higher foF2 for the rising branch compared to the
                  falling branch of solar cycle. However, this is not the case
                  in some individual months of some years. The noontime
                  hysteresis represents the hysteresis at other times of the
                  day qualitatively (as to sign) but not quantitatively. The
                  hysteresis appears to be relatively persistent from one
                  solar cycle to another solar cycle in spring but not in
                  autumn. A typical value for springtime hysteresis is about
                  0.5 MHz. The inclusion of hysteresis into longterm
                  ionospheric and radio wave propagation predictions remains
                  questionable.}
}

@ARTICLE{buresova2001,
  AUTHOR = {Buresova, D. and Lastovicka, J.},
  TITLE = {Changes in the F1 region electron density during geomagnetic
                  storms at low solar activity},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2001},
  VOLUME = {63},
  NUMBER = {5},
  PAGES = {537--544},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {This paper attempts to demonstrate the changes in the F1
                  layer ionization during geomagnetic storm. To analyze the
                  behavior of F1 region, we have selected eight rather strong
                  geomagnetic storms that occurred in different seasons in
                  1994-1997. Their course was similar and there were at least
                  three quiet days before each event. The electron density
                  profiles for these events, derived from all the available
                  ionograms of the Pruhonice station (50 degreesN, 14.6
                  degreesE), were analyzed in order to investigate electron
                  density variability at heights of 160-190 km. Spring/autumn
                  asymmetry of the effects in F1 region is found. We observed
                  no significant effect of an ionospheric storm in electron
                  density in the F1 region during spring geomagnetic storms,
                  while there is a substantial effect in autumn at 180 and 190
                  km heights. We have compared our results with those obtained
                  from ionograms of some other European ionospheric
                  stations. In general, the F1 region appears to be much more
                  stable than the F2 layer during ionospheric
                  storms. Substantial intra-hour variability was found in NmF2
                  during geomagnetic storms in daytime, while it was very weak
                  on the storm maximum day in F1 layer.}
}

@ARTICLE{buresova2002,
  AUTHOR = {Buresova, D. and Lastovicka, J. and Altadill, D. and Miro,
                  G.},
  TITLE = {Daytime electron density at the F1-region in Europe during
                  geomagnetic storms},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2002},
  VOLUME = {20},
  NUMBER = {7},
  PAGES = {1007--1021},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {This study attempts to demonstrate changes in the
                  ionospheric F1-region daytime ionization during geomagnetic
                  storms. The F1-region is explored using available data from
                  several European middle latitude and lower latitude
                  observatories and a set of geomagnetic storms encompassing a
                  range of seasons and solar activity levels. The results of
                  analysis suggest systematic seasonal and partly latitudinal
                  differences in the F1-region response to geomagnetic
                  storm. The pattern of the response of the F1-region at
                  higher middle latitudes, a decrease in electron density,
                  does not depend on the type of response of the F2-region and
                  on solar activity. A brief interpretation of these findings
                  is presented.}
}

@ARTICLE{butcher2005,
  AUTHOR = {Butcher, N.},
  TITLE = {Daily ionospheric forecasting service (DIFS) III},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2005},
  VOLUME = {23},
  NUMBER = {12},
  PAGES = {3591--3598},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  URL = {http://overview.sref.org/1432-0576/ag/2005-23-3591},
  ABSTRACT = {The daily variability of the ionosphere can greatly affect HF
                  or SATCOM communications. HF skywave operators plan frequency
                  schedules months in advance, however, they also require daily
                  knowledge of the ionospheric conditions in order to modify 
                  assignments. SATCOM operators also require daily information 
                  about the levels of scintillation, which are variations in 
                  phase, amplitude, polarisation and angle of arrival that can 
                  cause severe degradation of the received signal.

                  Using a number of ionosonde measurements and geomagnetic and 
                  solar values, a Daily Ionospheric Forecasting Service (DIFS) 
                  has been developed, which provides HF and SATCOM operators 
                  with daily forecasts of predicted ionospheric conditions. The
                  system uses in-house algorithms and an externally developed 
                  Global Ionospheric Scintillation Model (GISM) to generate HF 
                  and SATCOM forecasts. HF forecasts consist of a past summary 
                  and a forecast section, primarily displaying observed values 
                  and predicted categories for the Maximum Usable Frequency 
                  (MUF), as well as an Ionospheric Correction factor (ICF) that
                  can be fed into the ionospheric propagation prediction tool, 
                  WinHF. SATCOM forecasts give predictions of global 
                  scintillation levels, for the polar, mid and equatorial 
                  latitude regions. Thorough analysis was carried out on DIFS 
                  and the results conclude that the service gives good 
                  accuracy, with user feedback also confirming this, as well.}
}

@ARTICLE{cander04:_real-time_dynamic,
  AUTHOR = {Cander, L.R. and Hickford, J. and Tsagouri, I. and Belahaki,
                  A.},
  TITLE = {Real-time dynamic system for monitoring ionospheric
                  propagation conditions over Europe},
  JOURNAL = {Electronics Letters},
  PAGES = {224--226},
  YEAR = {2004},
  VOLUME = {40},
  NUMBER = {4},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  ABSTRACT = {Real-time measurements of the critical frequency of F-2
                  layer, foF(2), and the propagation factor for a 3000 kin
                  range, M(3000)F2 from four European Digisondes operating in
                  Athens, Rome, Chilton and Juliusruh and the Bz-component of
                  the interplanetary magnetic field, Bz-IMF, from the NASA
                  Advanced Composition Explorer (ACE) spacecraft mission are
                  combined for the development of a real-time dynamic system,
                  oriented to monitor the ionospheric propagation conditions
                  over Europe. The validity of the developed system in its
                  present operational form is investigated through the
                  analysis of two case study events. First results indicate a
                  temporal correlation between the Bz-IMF component
                  disturbances and the quantitative signature of ionospheric
                  disturbances at middle latitude, making the developed
                  facility a useful tool for modelling. and forecasting
                  ionospheric propagation conditions.}
}

@ARTICLE{cander98:_forec,
  AUTHOR = {Cander, L.R. and Mihajlovic, S.J.},
  TITLE = {Forecasting ionospheric structure during the great
                  geomagnetic storms},
  JOURNAL = {Journal of Geophysical Research},
  PAGES = {391--398},
  YEAR = {1998},
  VOLUME = {103},
  NUMBER = {A1},
  ABSTRACT = {Characteristics of midlatitude ionospheric disturbances
                  during several great geomagnetic storms have been
                  investigated using data from the European geomagnetic
                  observatories and ionospheric stations with the aim of
                  developing the local forecasting models, as part of the
                  prediction and retrospective ionospheric modeling over
                  Europe project. Based on the analysis of the geomagnetic
                  storms of February 6, 1986, and March 13, 1989, a detailed
                  picture of the local H component of geomagnetic field and
                  the ionospheric critical frequency f0F2 variations is
                  presented. The results show that f0F2 was dramatically
                  changed above or below the monthly median level in a
                  relatively narrow band about 15 of latitude and
                  30 longitude during the different phases of the
                  storms. These results support the view that day-to-day F
                  region ionospheric variability is essentially altered in
                  great storms. Consequences of those effects for short-term
                  modeling purposes are discussed.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}

@ARTICLE{cander98:_ionos,
  AUTHOR = {Cander, L.R. and Milosavljevic, M.M. and Stankovic, S.S. and
                  Tomasevic, S.},
  TITLE = {Ionospheric forecasting technique by artificial neural
                  network},
  JOURNAL = {Electronics Letters},
  PAGES = {1573--1574},
  YEAR = {1998},
  VOLUME = {34},
  NUMBER = {16},
  ABSTRACT = {An artificial neural network method is applied to the
                  development of an ionospheric forecasting technique for one
                  hour ahead. Comparisons between the observed and predicted
                  values of the critical frequency of the F 2 layer, foF2, and
                  the total electron content (TEC) are presented to show the
                  appropriateness of the proposed technique.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}

@ARTICLE{chan2002,
  AUTHOR = {Chan, A.H.Y. and Cannon, P.S.},
  TITLE = {Nonlinear forecasts of foF2: variation of model predictive
                  accuracy over time},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2002},
  VOLUME = {20},
  NUMBER = {7},
  PAGES = {1031--1038},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  ABSTRACT = {A nonlinear technique employing radial basis function neural
                  networks (RBF-NNs) has been applied to the short-term
                  forecasting of the ionospheric F2-layer critical frequency,
                  foF2. The accuracy of the model forecasts at a northern
                  mid-latitude location over long periods is assessed, and is
                  found to degrade with time. The results highlight the need
                  for the retraining and re-optimization of neural network
                  models on a regular basis to cope with changes in the
                  statistical properties of geophysical data sets. Periodic
                  retraining and re-optimization of the models resulted in a
                  reduction of the model predictive error by similar to0.1 MHz
                  per six months. A detailed examination of error metrics is
                  also presented to illustrate the difficulties encountered in
                  evaluating the performance of various prediction/forecasting
                  techniques.}
}

@ARTICLE{clilverd03,
  AUTHOR = {Clilverd, M. A. and Ulich, T. and Jarvis, M. J.},
  TITLE = {Residual solar cycle influence on trends in ionospheric
                  F2-layer peak height},
  JOURNAL = {Journal of Geophysical Research},
  YEAR = {2003},
  MONTH = {dec},
  VOLUME = {108},
  NUMBER = {A12},
  ABSTRACT = {The longest data sets available for estimating thermospheric
                  temperature trends are those from ground-based ionosondes,
                  which often begin during the International Geophysical Year
                  of 1957, close to a solar activity maximum. It is important
                  to investigate inconsistencies in trend estimates from these
                  data sets so that trends can be clearly determined. Here we
                  use selected ionosonde stations to show that one of the most
                  significant factors affecting the trend estimates is the
                  removal of the solar cycle. The stations show trend behavior
                  that is close to the behavior of a theoretical model of
                  damped harmonic oscillation. The ringing features are
                  consistent with the presence of solar cycle residuals from
                  the analysis with an amplitude of 2.5 km. Some stations do
                  not show trend behavior that is close to either the average
                  behavior of the stations studied here or the theoretical
                  model of oscillation. Four European stations (Poitiers,
                  Lannion, Juliusruh, and Slough), three of which are closely
                  located in western Europe, were analyzed with the
                  expectation that their trend should be similar. Only
                  Poitiers and Juliusruh showed an evolution that was close to
                  the average behavior of other stations, while the other two
                  were significantly different. The primary cause of this
                  appears to be changes in the M(3000)F2 parameter and
                  demonstrates the importance of incorporating consistency
                  checks between neighboring ionosondes into global
                  thermospheric trend estimates.},
  URL = {http://dx.doi.org/10.1029/2003JA009838},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}

@ARTICLE{dabas2003,
  AUTHOR = {Dabas, R.S. and Kersley, L.},
  TITLE = {Radio tomographic imaging as an aid to modeling of
                  ionospheric electron density},
  JOURNAL = {Radio Science},
  YEAR = {2003},
  VOLUME = {38},
  NUMBER = {3},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  URL = {http://dx.doi.org/10.1029/2001RS002514},
  ABSTRACT = {Models of the ionosphere, used in applications for the
                  prediction or correction of propagation effects on practical
                  radio systems, are often inadequate in their representation
                  of the structure and development of large-scale features in
                  the electron density. Over northern Europe, characterization
                  of the main trough presents particular problems for such
                  empirical or parameterized models and hence for radio
                  propagation forecasting and ionospheric mapping. Results are
                  presented from a study aimed at investigating the possible
                  role of radio tomographic imaging in adapting models to
                  yield a better representation of the ionosphere over
                  Europe. It is shown that use of radio tomography gives
                  better agreement with actual ionosonde data than can be
                  obtained from any of the models used alone. It is suggested
                  that the technique may have a possible role in the mapping
                  of ionospheric conditions in near-real time for future
                  systems applications.}
}

@ARTICLE{danilov2001:_f2region,
  AUTHOR = {Danilov, A.D.},
  TITLE = {F2-region response to geomagnetic disturbances},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  VOLUME = {63},
  NUMBER = {5},
  YEAR = {2001},
  PAGES = {441--449},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {The F2-region response to a geomagnetic storm usually called
                  a ionospheric storm is a rather complicated event. It
                  consists of the so-called positive an negative phases, which
                  have very complicated spatial and temporal behavior. During
                  the recent decade there was significant progress in
                  understanding this behavior. The principal features of the
                  positive and negative phase distribution and variations have
                  been explained on the basis of the principal concept: during
                  a geomagnetic disturbance there is an input of energy into
                  the polar ionosphere, which changes thermospheric
                  parameters, such as composition, temperature and
                  circulation. Composition changes directly influence the
                  electron concentration in the F2 region. The circulation
                  spreads the heated gas to lower latitudes. The conflict
                  between the storm-induced circulation and the regular one
                  determines the spatial distribution of the negative and
                  positive phases in various seasons. There are still problems
                  unsolved. The most acute ones are: the appearance of
                  positive phases before the beginning of a geomagnetic
                  disturbance, the occurrence of strong negative phases at the
                  equator, the role of vibrationally excited nitrogen in
                  forming the negative phase, and the relation of positive
                  phases to the dayside cusp. There are indications that the
                  f(o)F2 long-term trends revealed during the recent years may
                  be explained by long-term trends of the number of negative
                  ionospheric disturbances due to secular variations of the
                  geomagnetic activity.}
}

@ARTICLE{danilov2003,
  AUTHOR = {Danilov, A.D.},
  TITLE = {Long-term trends of foF2 independent of geomagnetic
                  activity},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2003},
  VOLUME = {21},
  NUMBER = {5},
  PAGES = {1167--1176},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {A detailed analysis of the foF2 data at a series of
                  ionospheric stations is performed to reveal long-term trends
                  independent of the long-term changes in geomagnetic activity
                  during the recent decades (nongeomagnetic trends). The
                  method developed by the author and published earlier is
                  used. It is found that the results for 21 out of 23 stations
                  considered agree well and give a relative nongeomagnetic
                  trend of -0.0012 per year (or an absolute nongeomagnetic
                  trend of about -0.012 MHz per year) for the period between
                  1958 and the mid-nineties. The trends derived show no
                  dependence on geomagnetic latitude or local time, a fact
                  confirming their independence of geomagnetic activity. The
                  consideration of the earlier period (1948-1985) for a few
                  stations for which the corresponding data are available
                  provides significantly lower foF2 trends, the difference
                  between the later and earlier periods being a factor of
                  1.6. This is a strong argument in favor of an anthropogenic
                  nature of the trends derived.}
}

@ARTICLE{danilov2001:_f2layer,
  AUTHOR = {Danilov, A.D. and Mikhailov, A.V.},
  TITLE = {F2-layer parameters long-term trends at the Argentine
                  Islands and Port Stanley stations},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2001},
  VOLUME = {19},
  NUMBER = {3},
  PAGES = {341--349},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {The ionospheric sounding data at two southern hemisphere
                  stations, the Argentine Islands and Port Stanley, are
                  analyzed using a method previously developed by the
                  authors. Negative trends of the critical frequency foF2 are
                  found for both stations. The magnitudes of the trends are
                  close to those at the corresponding (dose geomagnetic
                  latitude) stations of the northern hemisphere, as considered
                  previously by the authors. The values of the F2 layer height
                  hmF2 absolute trends Delta hmF2 are considered. The effect
                  of Delta hmF2 dependence on hmF2 found by Jarvis et
                  al. (1998) is reproduced. A concept is considered that
                  long-term changes of the geomagnetic activity may be an
                  important (if not the only) cause of all the trends of foF2
                  and hmF2 derived by several groups of authors. The
                  dependence of both parameters on the geomagnetic index Ap
                  corresponds to a smooth scheme of the ionospheric storm
                  physics and morphology; thus, a principal cause of the foF2
                  and hmF2 geomagnetic trends is most probably a trend found
                  in several publications in the number and intensity of
                  ionospheric storms.}
}

@ARTICLE{danilov2001:_long,
  AUTHOR = {Danilov, A.D. and Mikhailov, A.V.},
  TITLE = {Long-term trends in the F2-layer parameters at Argentine
                  Island and Port Stanley stations},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2001},
  VOLUME = {41},
  NUMBER = {4},
  PAGES = {488--496},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {The data of vertical ionospheric sounding at Argentine
                  Island and Port Stanley stations in the Southern Hemisphere
                  are analyzed using the method of long-term trends developed
                  by us earlier. The negative trends in the critical frequency
                  f(0)F2 have been found for both stations. The trend
                  magnitudes are similar to such magnitudes at stations
                  located at close geomagnetic latitudes in the Northern
                  Hemisphere and considered by us earlier. The values of the
                  absolute trends in the F2 layer height (hmF2, Delta hmF2)
                  are considered. The effect of the Delta hmF2 dependence on
                  hmF2 determined by Jarvis et al. [1998] is reproduced. A
                  conclusion is drawn that all trends in f(0)F2 and hmF2
                  derived by different groups of authors have a geomagnetic
                  origin and are a manifestation of the long-term changes in
                  the geomagnetic activity. It has been shown that the
                  dependence of both parameters on the geomagnetic index Ap
                  corresponds to a smoothed scheme of the physics and
                  morphology of the ionospheric storms. The trends in both
                  ionospheric parameters (f(0)F2 and hmF2) apparently reflect
                  the long-term trends in the number and intensity of the
                  ionospheric storms found in several publications.}
}

@ARTICLE{davis2001,
  AUTHOR = {Davis, C.J. and Clarke, E.M. and Bamford, R.A. and Lockwood,
                  M. and Bell, S.A.},
  TITLE = {Long term changes in EUV and X-ray emissions from the solar
                  corona and chromosphere as measured by the response of the
                  Earth's ionosphere during total solar eclipses from 1932 to
                  1999},
  JOURNAL = {Annales Geophysicae},
  PAGES = {263--273},
  YEAR = {2001},
  VOLUME = {19},
  PDF = {http://www.copernicus.org/EGU/annales/19/ag19/263.pdf},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  ABSTRACT = {Measurements of the ionospheric E region during total solar
                  eclipses in the period 1932-1999 have been used to
                  investigate the fraction of Extreme Ultra Violet and soft
                  X-ray radiation, phi, that is emitted from the limb corona
                  and chromosphere. The relative apparent sizes of the Moon
                  and the Sun are different for each eclipse, and techniques
                  are presented which correct the measurements and, therefore,
                  allow direct comparisons between different eclipses. The
                  results show that the fraction of ionising radiation emitted
                  by the limb corona has a clear solar cycle variation and
                  that the underlying trend shows this fraction has been
                  increasing since 1932. Data from the SOHO spacecraft are
                  used to study the effects of short-term variability and it
                  is shown that the observed long-term rise in phi has a
                  negligible probability of being a chance occurrence.}
}

@ARTICLE{davis2005,
  AUTHOR = {Davis, C.J. and Johnson, C.G.},
  TITLE = {Lightning-induced intensification of the ionospheric
                  sporadic E layer},
  JOURNAL = {Nature},
  PAGES = {799--801},
  YEAR = {2005},
  VOLUME = {435},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  ABSTRACT = {A connection between thunderstorms and the ionosphere has
                  been hypothesized since the mid-1920s(1). Several mechanisms
                  have been proposed to explain this connection(2-7), and
                  evidence from modelling(8) as well as various types of
                  measurements(9-14) demonstrate that lightning can interact
                  with the lower ionosphere. It has been proposed, on the
                  basis of a few observed events(15), that the ionospheric
                  'sporadic E' layer - transient, localized patches of
                  relatively high electron density in the mid-ionosphere E
                  layer, which significantly affect radio-wave propagation -
                  can be modulated by thunderstorms, but a more formal
                  statistical analysis is still needed. Here we identify a
                  statistically significant intensification and descent in
                  altitude of the mid-latitude sporadic E layer directly above
                  thunderstorms. Because no ionospheric response to
                  low-pressure systems without lightning is detected, we
                  conclude that this localized intensification of the sporadic
                  E layer can be attributed to lightning. We suggest that the
                  co-location of lightning and ionospheric enhancement can be
                  explained by either vertically propagating gravity waves
                  that transfer energy from the site of lightning into the
                  ionosphere, or vertical electrical discharge, or by a
                  combination of these two mechanisms.}
}

@ARTICLE{davis2000,
  AUTHOR = {Davis, C.J. and Lockwood, M. and Bell, S.A. and Smith,
                  J.A. and Clarke, E.M.},
  TITLE = {Ionospheric measurements of relative coronal brightness
                  during the total solar eclipses of 11 August, 1999 and 9
                  July, 1945},
  JOURNAL = {Annales Geophysicae},
  PAGES = {182--190},
  YEAR = {2000},
  VOLUME = {18},
  NUMBER = {2},
  ABSTRACT = {Swept-frequency (1-10 MHz) ionosonde measurements were made
                  at Helston, Cornwall (50∘06'N, 5∘18'W) during
                  the total solar eclipse on August 11, 1999. Soundings were
                  made every three minutes. We present a method for estimating
                  the percentage of the ionising solar radiation which remains
                  unobscured at any time during the eclipse by comparing the
                  variation of the ionospheric E-layer with the behaviour of
                  the layer during a control day. Application to the ionosonde
                  date for 11 August, 1999, shows that the flux of solar
                  ionising radiation fell to a minimum of 252% of the
                  value before and after the eclipse. For comparison, the same
                  technique was also applied to measurements made during the
                  total solar eclipse of 9 July, 1945, at S\"ormj\"ole
                  (63∘68'N, 20∘20'E) and yielded a corresponding
                  minimum of 162%. Therefore the method can detect
                  variations in the fraction of solar emissions that originate
                  from the unobscured corona and chromosphere. We discuss the
                  differences between these two eclipses in terms of the
                  nature of the eclipse, short-term fluctuations, the sunspot
                  cycle and the recently-discovered long-term change in the
                  coronal magnetic field.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  PDF = {http://www.copernicus.org/EGS/annales/18/ag18/182.pdf}
}

@ARTICLE{deminov03:_long_E,
  AUTHOR = {Deminov, M.G. and Kolesnik, A.G. and Leshchenko, L.N. and
                  Sitnov, Y.S. and Tsybikov, B.B.},
  TITLE = {Climatic variations in the ionospheric E-layer noon critical
                  frequencies at midlatitudes},
  JOURNAL = {Annales Geophysicae},
  PAGES = {356--362},
  YEAR = {2003},
  VOLUME = {43},
  NUMBER = {3},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {The noon median values of the E-layer critical frequency
                  (foE) measured at Slough/Chilton (1931-1997), Moscow
                  (1946-1997), and Tomsk (1938-1997) stations have been
                  analyzed. New regularities in the foE climatic (long-term)
                  variations, the regression dependences of these variations
                  on the Wolf numbers averaged over 11 years (R-11, a global
                  factor), and the surface air temperature near a particular
                  station minus the temperature at the ocean-continent
                  boundary (DeltaT(11), a regional factor) have been
                  determined. The global factor predominates for
                  Slough/Chilton station located in the vicinity of the
                  ocean-continent boundary. The additional regression
                  dependence of foE on DeltaT(11) is substantial and
                  significant for the continental stations (the continental
                  effect). For Tomsk, this effect is even a predominant cause
                  of climatic variations in foE.}
}

@ARTICLE{farges2001,
  AUTHOR = {Farges, T. and Jodogne, J.C. and Bamford, R. and Le Roux,
                  Y. and Gauthier, F. and Vila, P.M. and Altadill, D. and
                  Sole, J.G. and Miro, G.},
  TITLE = {Disturbances of the western European ionosphere during the
                  total solar eclipse of 11 August 1999 measured by a wide
                  ionosonde and radar network},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2001},
  VOLUME = {63},
  NUMBER = {9},
  PAGES = {915--924},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {},
  ABSTRACT = {The 11 August 1999 Solar eclipse totality path ran across
                  western Europe at near-constant latitudes of about 49
                  degreesN. It occurred at mid-time of a sequence of three
                  days with steady solar wind and quiet magnetospheric
                  conditions. Its response was observed by a score of
                  ionospheric facilities, which will provide high-resolution
                  probing of the various disturbances. First results allow us
                  to compare the time fluctuations at various distances from
                  totality on the eclipse and adjacent days, inside a 5
                  degrees West to 5 degrees East longitude area. In this
                  preliminary work the foF1 and foF2 time changes are
                  presented in contour maps on a 50 km size grid. They show
                  the expected longitude transit of eclipse perturbation. We
                  venture brief comments on the eclipse-own signatures as
                  separate from the various wave oscillations detected prior
                  to eclipse time by 12.4 MHz panoramic azimuth scans of the
                  Losquet radar near Lannion (Brittanny).}
}

@ARTICLE{forbes2000,
  AUTHOR = {Forbes, J.M. and Palo, S.E. and Zhang, X.L.},
  TITLE = {Variability of the ionosphere},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2000},
  VOLUME = {62},
  NUMBER = {8},
  PAGES = {685--693},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {Hourly foF2 data from over 100 ionosonde stations during 1967-89
              are examined to quantify F-region ionospheric variability, and
              to assess to what degree the observed variability may be
              attributed to various sources, i.e., solar ionizing Aux,
              meteorological influences, and changing solar wind
              conditions. Our findings are as follows. Under quiet geomagnetic
              conditions (K-p < 1), the 1-sigma (sigma is the standard
              deviation) variability of N-max about the mean is
              approx. +/-25-35% at 'high frequencies' (periods of a few hours
              to 1-2 days) and approx. +/-15-20% at 'low frequencies' (periods
              approx. 2-30 days), at all latitudes. These values provide a
              reasonable average estimate of ionospheric variability mainly
              due to "meteorological influences" at these frequencies. Changes
              in N-max due to variations in solar photon flux, are, on the
              average, small in comparison at these frequencies. Under quiet
              conditions for high-frequency oscillations, N-max is most
              variable at anomaly peak latitudes. This may reflect the
              sensitivity of anomaly peak densities to day-to-day variations
              in F-region winds and electric fields driven by the E-region
              wind dynamo. Ionospheric variability increases with magnetic
              activity at all latitudes and for both low and high frequency
              ranges, and the slopes of all curves increase with
              latitude. Thus, the responsiveness of the ionosphere to
              increased magnetic activity increases as one progresses from
              lower to higher latitudes. For the 25% most disturbed conditions
              (K-p > 4), the average 1-sigma variability of N-max about the
              mean ranges from approx. +/-35% (equator) to approx. +/-45%
              (anomaly peak) to approx. +/-55% (high-latitudes) for high
              frequencies, and from approx. +/-25% (equator) to approx. +/-45%
              (high-latitudes) at low frequencies. Some estimates are also
              provided on N-max variability connected with annual, semiannual
              and Ii-year solar cycle variations. (C) 2000 Elsevier Science
              Ltd. All rights reserved.}
}

@ARTICLE{francis01:_predic,
  AUTHOR = {Francis, N.M. and Brown, A.G. and Cannon, P.S. and
                  Broomhead, D.S.},
  TITLE = {Prediction of the hourly ionospheric parameter, foF2,
                  incorporating a novel nonlinear interpolation technique to
                  cope with missing data points},
  JOURNAL = {Journal of Geophysical Research},
  PAGES = {30077-30084},
  YEAR = {2001},
  MONTH = {dec},
  VOLUME = {106},
  NUMBER = {A12},
  URL = {http://dx.doi.org/10.1029/2000JA002227},
  ABSTRACT = {A technique for neural network time series prediction using
                  radial basis functions, where the input data contain a
                  significant proportion of missing points, is developed. This
                  technique is intended to model the data while simultaneously
                  providing a means of minimizing the impact upon the model of
                  the missing points that are typical of geophysical time
                  series. The two issues are inextricably entwined because
                  missing data points have a significant impact upon the
                  performance of data-derived models in terms of prediction
                  availability and accuracy. The core of the technique is a
                  nonlinear interpolation scheme that assigns values to gaps
                  in the input time series. Each missing point is interpolated
                  such that the error introduced into any specific predictive
                  function is minimized. This interpolative technique has a
                  general application in any instance where the effects of
                  interpolation upon a given analysis process need to be
                  minimized or a complete time series needs to be constructed
                  from incomplete data. The technique has been applied to the
                  prediction of fOF2 from Slough, United Kingdom. The
                  resultant model prediction root-mean-square (RMS) error is
                  shown to be 2.3% better than using recurrence interpolation
                  (in terms of overall model accuracy rather than relative to
                  each other), 3.8% better than using persistence
                  interpolation, and 34.3% better than not using any
                  interpolation. Utilizing the interpolation algorithm lowers
                  the RMS error by 26% when incomplete data, in addition to
                  complete data, are used as an input to both the interpolated
                  and the uninterpolated models.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}

@ARTICLE{garcia-fernandez2003,
  AUTHOR = {Garcia-Fernandez, M. and Hernandez-Pajares, M. and Juan,
                  J.M. and Sanz, J. and Orus, R. and Coisson, P. and Nava,
                  B. and Radicella, S.M.},
  TITLE = {Combining ionosonde with ground GPS data for electron
                  density estimation},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2003},
  VOLUME = {65},
  NUMBER = {6},
  PAGES = {683--691},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {Dual frequency Global Positioning System (GPS) receivers
                  provide integrated total electron content (TEC) along the
                  ray path (slant TEC, affected by a bias). By inverting this
                  observable, it is possible to obtain the vertical total
                  electron content with some assumptions about the horizontal
                  structure of the ionosphere. The large number of permanent
                  receivers distributed around the world provide enough
                  information to obtain such TEC observables with high spatial
                  and temporal resolutions. Nevertheless, the geometry (mainly
                  vertical) of the ground GPS observations does not allow to
                  solve the vertical structure of electron density of the
                  ionosphere. Mixing different kinds of complementary data in
                  a tomographic context helps to overcome this
                  problem. Several works have obtained successful results
                  achieved by combining occultation and ground GPS data to
                  estimate the local three-dimensional structure of
                  ionospheric electron density. This paper proposes the use of
                  just ground data to obtain similar or better results. To do
                  this, the ground GPS data are mixed with vertical profiles
                  of electron density derived from ionosonde data instead of
                  GPS occultation observations. In this paper, the
                  complementarity between vertical profiles of electron
                  density (estimated using the NeQuick model) and ground GPS
                  data (from GPS IGS permanent network) are shown as well as
                  the performance of the resulting combination.}
}

@ARTICLE{gilbert1988,
  AUTHOR = {Gilbert, John D. and Smith, Richard W.},
  TITLE = {A comparison between the automatic ionogram scaling system
                  ARTIST and the standard manual method},
  JOURNAL = {Radio Science},
  PAGES = {968--974},
  YEAR = {1988},
  MONTH = NOV,
  VOLUME = {23},
  NUMBER = {6},
  ABSTRACT = {Data from midlatitude ionograms scaled by the computer
                  system, ARTIST, are compared with data from the standard
                  manual method. Differences between the scaled values for
                  foF2 and M(3000)F2 are presented for five periods of low
                  sunspot activity between 1984 and 1986. It is found that the
                  ARTIST system provides acceptable data about 93 pct of the
                  time. The system does not perform as well in summer due to
                  the presence of blanketing-type Es and the proximity of foF2
                  to foF1.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}

@ARTICLE{gulyaeva05:_night,
  AUTHOR = {Gulyaeva, T. and Stanislawska, W.},
  TITLE = {Night-day imprints of ionospheric slab thickness during geomagnetic storm},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = 2005,
  VOLUME = 67,
  NUMBER = 14,
  PAGES = {1307--1314},
  MONTH = {September},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1016/j.jastp.2005.07.006},
  ABSTRACT = {Spatial maps of the ionosphere-plasmasphere slab thickness (T) were generated as a ratio of the total electron content (TEC) to the F-region peak electron density (NmF2) at 1 degrees spaced grid points from the instantaneous maps of TEC and foF2 at latitudes 35 degrees to 70 degrees N, and longitudes -10 degrees to 40 degrees E. Data of 23 observatories are used for the construction of TEC and foF2 maps with Kriging technique from independent networks of GPS-TEC and ionosonde observations at solar minimum (1995-1996) and maximum (2002) under quiet and disturbed magnetic conditions. The net-weight factor (omega) is introduced as a ratio of disturbance to quietness representing area mean TEC,foF2 and tau for a particular day and time normalized by relevant monthly median value. Analysis of w evolution for TEC, foF2 and T maps have revealed that TEC and foF2 depletion is accompanied by positive increment of slab thickness for more than 48 hrs during the magnetic storm at solar maximum but T enhancement is shorter and delayed by 12 to 24 hrs regarding the storm onset at solar minimum. The slab thickness positive increment at the main,phase of geomagnetic storm has been associated with relevant increase of the real thickness of the topside ionosphere. To estimate-the upper boundary of the ionosphere the International Reference Ionosphere expanded towards the plasmasphere (IRI*) is modified to assimilate the ionosonde F2 layer peak and the GPS-T.EC observations. Slab thickness is decomposed in three parts (the bottomside and topside ionosphere, and the plasmasphere). Eliminating the plasmasphere part from the total slab thickness, we obtain the ratio of bottomside slab thickness to the real thickness below the F2 layer peak. Assuming that this ratio is also valid above the F2 layer peak, we obtain the topside boundary of the ionosphere varying from 500 km by day to 2300km by night. (c) 2005 Elsevier Ltd. All rights reserved.}
}

@ARTICLE{heaton2001,
  AUTHOR = {Heaton, J.A.T. and Cannon, P.S. and Rogers, N.C. and
                  Mitchell, C.N. and Kersley, L.},
  TITLE = {Validation of electron density profiles derived from oblique
                  ionograms over the United Kingdom},
  JOURNAL = {Radio Science},
  YEAR = {2001},
  VOLUME = {36},
  NUMBER = {5},
  PAGES = {1149--1156},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  URL = {http://dx.doi.org/10.1029/1999RS002423},
  ABSTRACT = {Inversion algorithms are available to derive the vertical
                  electron density profile at the midpoint of an oblique
                  sounder path. The techniques open up the possibility of
                  monitoring the ionosphere at otherwise inaccessible
                  locations, such as over sea or inhospitable terrain. A new
                  method of monitoring the ionosphere based on radio
                  tomography can be used to create two-dimensional images of
                  electron density. The results in this paper compare midpoint
                  profiles derived from oblique ionograms with corresponding
                  profiles obtained from tomographic images of electron
                  density and from a vertical ionospheric sounder. The
                  comparisons illustrate the oblique sounder inversion
                  technique and its inherent limitations. The results provide
                  useful information on the complementary nature of the
                  separate ionospheric measurement techniques and have
                  implications for the use of these measurements as inputs to
                  real-time ionospheric models.}
}

@ARTICLE{ivanov-kholodnyi2000,
  AUTHOR = {Ivanov-Kholodnyi, G.S. and Chertoprud, V.E.},
  TITLE = {Peculiarities of solar-ionospheric relationships during
                  minima and maxima of 27-day variations in F-10.7},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2000},
  VOLUME = {40},
  NUMBER = {6},
  PAGES = {681--686},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {Based on a 37-year-long (1958-1994) series of hourly
                  measurements of the ionospheric E-region critical frequency
                  f(0)E at four stations (Moscow, Kaliningrad, Slough, and
                  Boulder), we determine the ionization index I-E (the fourth
                  power of the normalized critical frequency) and analyze its
                  correlation with solar radio flux F-10.7 during maxima and
                  minima of 27-day variations in F-10.7 The coefficients of
                  the linear regression equation that describes the
                  correlation of I-E with F-10.7 have been found to differ
                  markedly during these periods and exhibit semiannual
                  variations. Possible causes of these effects are discussed.}
}

@ARTICLE{jarvis2002,
  AUTHOR = {Jarvis, M.J. and Clilverd, M.A. and Ulich, T.},
  TITLE = {Methodological influences on F-region peak height trend
                  analyses},
  JOURNAL = {Physics and Chemistry of the Earth},
  YEAR = {2002},
  VOLUME = {27},
  NUMBER = {6--8},
  PAGES = {589--594},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  ABSTRACT = {Published estimates of the trend in hmF2 using data from
                  ionosondes over the last 30-40 years range from +0.8 to -0.6
                  km yr(-1) and are subject to the influence of several
                  factors. These are considered here based upon an analysis of
                  two southern hemisphere geomagnetically mid-latitude
                  stations, Argentine Islands and Port Stanley. The influence
                  of the equation used to calculate hmF2 at these stations can
                  result in variations of +/-0.2 km yr(-1); choice of solar
                  proxy has a small influence on the end result, where using
                  E10.7 instead of F10.7 produces changes of -0.04 km yr(-1);
                  neglecting any trends in geomagnetic activity can produce
                  variations of +0.03 to +0.2 km yr(-1) at the two
                  mid-latitude stations considered in this paper; for datasets
                  of 30-40 years length ringing due to long memory processes
                  can produce +/-0.2 km yr(-1) variability; the phase of the
                  11-year solar cycle, and its harmonics, captured by the
                  datasets can cause variability of +/-0.5 km yr(-1); and the
                  neglect of local time variations in thermospheric wind
                  conditions could result in +0.2 km yr(-1) for analysis which
                  only considers local midday data. The Argentine Islands and
                  Port Stanley datasets show ringing terms that are still
                  converging towards trend results of -0.25 to -0.30 km
                  yr(-1), which are in close agreement with the satellite drag
                  trend estimates.}
}

@ARTICLE{jarvis98:_south_f,
  AUTHOR = {Jarvis, M.J. and Jenkins, B. and Rodgers, G.A.},
  TITLE = {Southern hemisphere observations of a long-term decrease in
                  F region altitude and thermospheric wind providing possible
                  evidence for global thermospheric cooling},
  JOURNAL = {Journal of Geophysical Research},
  PAGES = {20775--20787},
  YEAR = {1998},
  VOLUME = {103},
  NUMBER = {A9},
  ABSTRACT = {F-region peak heights, derived from ionospheric scaled
                  parameters through 38-year data series from both Argentine
                  Islands (65 S, 64 W) and Port Stanley (52 S, 58 W) have been
                  analysed for signatures of secular change. Long-term changes
                  in altitude, which vary with month and time of day, were
                  found at both sites. The results can be interpreted either
                  as a constant decrease in altitude combined with a
                  decreasing thermospheric wind effect, or a constant decrease
                  in altitude which is altitude-dependent. Both
                  interpretations leave inconsistencies when the results from
                  the two sites are compared. The estimated long-term decrease
                  in altitude is of a similar order of magnitude to that which
                  has been predicted to result in the thermosphere from
                  anthropogenic change related to greenhouse gases. Other
                  possibilities should not, however, be ruled out.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}

@ARTICLE{jones04,
  AUTHOR = {Jones, T. B. and Wright, D. M. and Milner, J. and Yeoman,
                  T. K. and Reid, T. and Senior, A. and Martinez, P.},
  TITLE = {The detection of atmospheric waves produced by the total
                  solar eclipse 11 August 1999},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  PAGES = {363-374},
  YEAR = {2004},
  MONTH = MAR,
  VOLUME = {66},
  NUMBER = {5},
  ABSTRACT = {In previous attempts to detect eclipse-induced AGW, it has
                  always been difficult to establish a direct link between
                  individual waves and a specific source. This study reports
                  observations of travelling ionospheric disturbances made in
                  the UK at the time of the total solar eclipse of 11 August
                  1999. The speed and direction of the waves were estimated by
                  a four-station array using the HF Doppler technique. In
                  addition, the wave observations were supported by two other
                  propagation paths, one in the north of England close to the
                  main array and the other further afield, between the UK and
                  Sweden. The AGW activity following the eclipse totality was
                  different to the background waves detected before this time
                  in amplitude, speed and direction. The velocity vectors are
                  consistent with a generating mechanism for the waves based
                  on the supersonic passage of the cooled region of the
                  atmosphere during the eclipse.},
  UKSSDC_I = {},
  UKSSDC_D = {},
  UK_FIRST = {}
}

@ARTICLE{kalinin2003,
  AUTHOR = {Kalinin, U.K. and Romanchuk, A.A. and Sergeenko, N.P. and
                  Shubin, V.N.},
  TITLE = {The large-scale isolated disturbances dynamics in the main
                  peak of electronic concentration of ionosphere},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2003},
  VOLUME = {65},
  NUMBER = {11--13},
  PAGES = {1175--1177},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {The vertical sounding data at chains of ionosphere stations
                  are used to obtain relative variations of electron
                  concentration in the F2 ionosphere region. Specific isolated
                  traveling large-scale irregularities are distinguished in
                  the diurnal succession of the f(c)F2 relative variations
                  records. The temporal shifts of the irregularities at the
                  station chains determine their motion velocity (of the order
                  of speed of sound) and spatial scale (of order of 3000-5000
                  kin, the trajectory length being up to 10000 km). The motion
                  trajectories of large-scale isolated irregularities which
                  had preceded the earthquakes are reconstructed.}
}

@ARTICLE{korenkov2002,
  AUTHOR = {Korenkov, Y.N. and Klimenko, V.V. and Bessarab, F.S. and
                  Ferster, M.},
  TITLE = {Modeling of the ionospheric F2-region parameters in quiet
                  conditions on January 21-22, 1993},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2002},
  VOLUME = {42},
  NUMBER = {3},
  PAGES = {350--359},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {Results of the simulation of ionospheric parameters over
                  American stations (Millstone Hill, Arecibo, Port Stanley,
                  and the Argentine Islands) and the European EISCAT station
                  are presented. The calculations have been performed with the
                  help of the global self-consistent model of the
                  thermosphere, ionosphere, and protonosphere (GSM TIP) for
                  January 21, 1993. The day considered, entering into the
                  LTCS-9 campaign period, was characterized by quiet
                  geomagnetic conditions and moderate solar activity. It is
                  shown that the calculated and observed values of foF2 and
                  T-e agree satisfactorily if we take into account soft
                  electron precipitation in the diffuse zone, located
                  equatorward of the main auroral precipitation zone, and in
                  the South American geomagnetic anomaly zone.}
}

@ARTICLE{kouris98:_solar_m_f2,
  AUTHOR = {Kouris, S.S. and Bradley, P.A. and Dominici, P.},
  TITLE = {Solar-cycle variation of the daily foF2 and M(3000)F2},
  JOURNAL = {Annales Geophysicae},
  PAGES = {1039--1042},
  YEAR = {1998},
  VOLUME = {16},
  NUMBER = {8},
  ABSTRACT = {Daily values of the ionospheric characteristics foF2 and
                  M(3000)F2 for a given hour and month are correlated with the
                  corresponding daily values of sunspot number using measured
                  data collected at seven European locations. The significance
                  of applying different-order polynomials is considered and
                  the times are confirmed when the higher-order terms are
                  important. Mean correlation coefficients for combined data
                  sets over all hours, months and stations are determined,
                  together with the standard errors of estimates. Comparisons
                  are made with corresponding figures for monthly median
                  values derived from the same data sets.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {}
}

@ARTICLE{krasnov2003,
  AUTHOR = {Krasnov, V.M. and Drobzheva, Y.V. and Venart, J.E.S. and
                  Lastovicka, J.},
  TITLE = {A re-analysis of the atmospheric and ionospheric effects of
                  the Flixborough explosion},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2003},
  VOLUME = {65},
  NUMBER = {11--13},
  PAGES = {1205--1212},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {The ionospheric record of the 1974 cyclohexane vapour cloud
                  explosion (VCE) accident near Flixborough is re-examined in
                  light of a new theory used to describe the acoustic field in
                  the atmosphere and ionosphere caused by explosions on the
                  ground. The reconstructed oblique Doppler sounding records
                  from six radio traces agree remarkably well with
                  experimental results when a around source explosion yield of
                  283+/-38 tons of TNT is utilized. This result, when compared
                  to the detonation of large hydrocarbon fuel-drop-air clouds,
                  suggests that only 14+/-2 tons of cyclohexane was involved
                  in the explosion. Additionally the time of the explosion
                  determined from the model, 15:52:08+/-6, agrees, within the
                  mutual uncertainty, with that determined seismically,
                  15:52:15.5+/-2 LIT. The precision in the value of the yield
                  and accuracy of the time of the explosion validates the
                  model used to describe the propagation of acoustic waves by
                  taking into account expansion, absorption, and non-linear
                  and inhomogeneous effects in the atmosphere and ionosphere.}
}

@ARTICLE{kutiev01,
  AUTHOR = {Kutiev, I. and Muhtarov, P.},
  TITLE = {Modeling of midlatitude F region response to geomagnetic
                  activity},
  JOURNAL = {Journal of Geophysical Research},
  PAGES = {15501-15510},
  YEAR = {2001},
  MONTH = {aug},
  VOLUME = {106},
  NUMBER = {A8},
  ABSTRACT = {An empirical model is developed to describe the variations
                  of midlatitude F region ionization along all longitudes
                  within the dip latitude band
                  (30%G–%@55%G %@N),
                  induced by geomagnetic activity, by using the relative
                  deviations () of the F region critical frequency f0F2
                  from its monthly median. The geomagnetic activity is
                  represented by the Kp index. The main statistical
                  relationship between  and Kp is obtained by using 11
                  years of data from 26 midlatitude ionosondes. The
                  statistical analysis reveals that the average dependence of
                   on Kp is quadratic, the average response of the
                  ionosphere to geomagnetic forcing is delayed with a time
                  constant T of about 18 hours, and the instantaneous
                  distribution of  along local times can be assumed
                  sinusoidal. A continuity equation is written for  with
                  the production term being a function of Kp modulated
                  by a sinusoidal function of local time and the loss
                  term proportional to  with a loss coefficient
                  =1/T. A new, modified function of geomagnetic activity
                  (Kf) is introduced, being proportional to  averaged over
                  all longitudes. The model  is defined by two standing
                  sinusoidal waves with periods of 24 and 12 hours, rotating
                  synchronously with the Sun, modulated by the modified
                  function Kf. The wave amplitudes and phases, as well as
                  their average offset, are obtained by fitting to the data. A
                  new error estimate called prediction efficiency
                  (Peff) is used, which assigns equal weights to the model
                  errors at all deviations of data from medians. The
                  prediction efficiency estimate gives a gain of accuracy of
                  29%.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{kutiev2003,
  AUTHOR = {Kutiev, I. and Muhtarov, P.},
  TITLE = {Empirical modeling of global ionospheric f(o)F(2) response
                  to geomagnetic activity},
  JOURNAL = {Journal of Geophysical Research},
  YEAR = {2003},
  VOLUME = {108},
  NUMBER = {A1},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1029/2001JA009134},
  ABSTRACT = {[1] The authors expand the previously developed midlatitude
                  model, providing the relative deviation of f(o)F(2) from its
                  monthly median value as a function of local time and Kp, to
                  the global scale. To achieve this, 55 ionosonde stations,
                  having at least 11 years of continuous data, have been
                  selected, and the model was applied to the data from each
                  station separately. Data from each station were grouped into
                  12-month bins, every bin containing all the available hourly
                  data within the respective month of the year. The model
                  considers the distribution of the relative deviation along
                  the local time at any fixed moment as composed of a diurnal
                  and a semidiurnal waves, expressed by five parameters: daily
                  mean (average offset), diurnal and semidiurnal amplitudes
                  and phases. The model expression is scaled by a modified
                  function of Kp, which reflects the delayed reaction of foF2
                  to Kp changes. The model parameters are determined by
                  fitting the model expression to the data in each bin. Their
                  distribution along the geomagnetic latitude is obtained in
                  three longitude sectors: North America-South America,
                  Europe-Africa, and East Asia-Australia. The seasonal
                  symmetry of model parameters in the Northern and Southern
                  Hemispheres, which is found to be acceptable, allows the use
                  of parameter values from both hemispheres in obtaining their
                  latitudinal profiles. In order to produce global
                  distribution of each of the model parameters, the respective
                  latitudinal profiles from the three sectors were averaged
                  and approximated by analytical expressions.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{lastovicka2005,
  AUTHOR = {Lastovicka, J.},
  TITLE = {On the role of solar and geomagnetic activity in long-term
                  trends in the atmosphere-ionosphere system},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2005},
  VOLUME = {67},
  NUMBER = {1--2},
  PAGES = {83--92},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {The long-term continuous increase of greenhouse gas
                  concentration in the atmosphere and other anthropogenic
                  influences represent serious threat for human
                  civilization. Therefore, it is necessary to determine the
                  long-term trends and changes in the atmosphere-ionosphere
                  system. The observed long-term trends in the 20th century
                  might be. however, influenced by contribution of Sun's
                  origin, and the process of determination of anthropoger c
                  trends from observational data may be "spoilt" by the
                  11-year solar cycle. The role of solar/geomagnetic activity
                  in long-term trends in various regions of the
                  atmosphere/ionosphere system is briefly reviewed for the
                  first time. The ways; of avoiding or at least diminishing
                  the effect of solar cycle on trend determination are
                  mentioned. As for the possible solar and geomagnetic
                  activity responsibility for part of the observed long-term
                  trends. the two main conclusions are as follows: (i) The
                  role of solar and geomagnetic activity in the observed
                  long-term trends decreases with decreasing altitude from the
                  F-region ionosphere down to the troposphere. (ii) In the
                  20th century the role of solar and geomagnetic activity in
                  the observed long-term trends/changes was decreasing from
                  its beginning towards its end.}
}

@ARTICLE{lastovicka2003,
  AUTHOR = {Lastovicka, J. and Krizan, P. and Sauli, P. and Novotna, D.},
  TITLE = {Persistence of the planetary wave type oscillations in foF2
                  over Europe},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2003},
  VOLUME = {21},
  NUMBER = {7},
  PAGES = {1543--1552},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {Planetary waves are oscillations of very predominantly
                  tropospheric origin with typical periods of about 2-30
                  days. Their dominant zonal wave numbers are 1, 2 and 3,
                  i.e. the waves are of large-scale (global) character. The
                  planetary wave type oscillations have been observed in the
                  lower and middle atmosphere but also in the ionosphere,
                  including the ionospheric F2-layer. Here, we deal only with
                  the oscillations analyzed for four European stations over a
                  solar cycle with the use of the Meyer and Morlet wavelet
                  transforms. Waves with periods near 5, 10 and 16 days are
                  studied. Only events with a duration of three wave-cycles
                  and more are considered. The 5-day period wave events
                  display a typical duration of 4 cycles, while 10- and 16-day
                  wave events are less persistent, with a typical duration of
                  about 3.5 cycles and 3 cycles, respectively. The persistence
                  pattern in terms of number of cycles and in terms of number
                  of days is different. In terms of number of cycles, the
                  typical persistence of oscillations decreases with
                  increasing period. On the other hand, in terms of number of
                  days the typical persistence evidently increases with
                  increasing period. The spectral distribution of event
                  duration is too broad to allow for a reasonable prediction
                  of event duration. Thus, the predictability of the planetary
                  wave type oscillations in foF2 seems to be very
                  questionable.}
}

@ARTICLE{li2003,
  AUTHOR = {Li, X.Y. and Yu, T.},
  TITLE = {Annual and semi-annual variations of the observed foF2 in a
                  high solar activity year},
  JOURNAL = {Terrestrial Atmospheric and Oceanic Sciences},
  YEAR = {2003},
  PAGES = {41--62},
  VOLUME = 14,
  NUMBER = 1,
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {By the Fourier series expanding method, the observed F2
                  layer critical frequencies (foF2) globally over 70 stations
                  in a high solar activity year of 1958, are used to analyze
                  the annual and semi-annual variations of foF2, and the world
                  wide distribution features of their amplitude and phase in
                  daytime and nighttime are studied in detail. The results for
                  foF2 annual and semi-annual variation are summarized as
                  follows. The midnight (2:00 LT) foF2 annual variations are
                  noticeable in both hemispheres at mid-high latitudes, and
                  their amplitudes are slightly larger in far pole regions
                  than in near pole regions. Generally, at most stations, the
                  midnight foF2 reach the maximum in summer, and no winter
                  anomaly can be discerned. While in daytime (14:00 LT), there
                  are pronounced annual variations with large amplitude in
                  both hemispheres at mid-high latitudes. After carefully
                  studying their phases, we find that these annual variations
                  usually peak in winter, which indicate all the variations
                  are classic winter anomaly. However, the winter anomaly is
                  very weak in the equatorial zone and not even perceivable in
                  South America. Moreover, the amplitude of daytime foF2
                  semi-annual variation is generally small in near pole
                  regions and large in far poles region of both
                  hemispheres. Compared with their annual component, the
                  semi-annual variations in the tropical region are
                  significant. Their phase distributions reveal that the
                  semi-annual variation usually peaks in March and April. In
                  order to explain the results mentioned above, we studied the
                  atomic molecular ratio [O/N-2] and confirmed that the noon
                  foF2 annual variations prevailing in mid-high latitudes are
                  caused largely by the annual variation of [O/N-2]. As the
                  noon foF2 semi-annual variations pronounced in far pole
                  regions, we should consider the contribution of [O/N-2], the
                  solar zenith angle, the solar-driven low/mid-latitude
                  thermospheric circulation and the magnetospherically driven
                  high-latitude circulation. Moreover, we suggest that foF2
                  semi-annual variations appearing in the equatorial zone are
                  closely related to other semi-annual variations in the upper
                  atmosphere, such as the semi-annual variation of [O/N-2],
                  the thermospheric circulation, the geomagnetic activities
                  and even the ionospheric electrical field.}
}

@ARTICLE{liulb04,
  AUTHOR = {Liu, L. and Luan, X. and Wan, W. and Lei, J. and Ning, B.},
  TITLE = {Solar activity variations of equivalent winds derived from
                  global ionosonde data},
  JOURNAL = {Journal of Geophysical Research},
  YEAR = {2004},
  MONTH = {dec},
  VOLUME = {109},
  NUMBER = {A12},
  URL = {http://dx.doi.org/10.1029/2004JA010574},
  ABSTRACT = {The equivalent winds at the F layer peak are derived from
                  global ionosonde data to investigate their solar activity
                  variations. With increasing solar activity, the derived
                  equivalent winds are found of nonlinearly decreased diurnal
                  amplitudes in all seasons at most stations. This implies
                  that the increase in ion drag more than compensates for
                  pressure gradients and thus restrains the diurnal amplitude
                  at high solar activity. The diurnal phase of the derived
                  equivalent winds generally shifts later at higher solar
                  activity. It is the first time to explicitly report this
                  striking feature that emerged at so many stations. Another
                  pronounced feature is that the diurnal phase has a
                  summer-winter difference. The diurnal phases at most
                  stations in the Northern Hemisphere are later in winter than
                  in summer at higher solar activity. Furthermore, a decrease
                  in the semidiurnal amplitudes of equivalent winds with
                  increasing solar activity is evident in winter over most
                  stations considered and in other seasons at stations with a
                  lower dip, but the decrease trend becomes weak in other
                  seasons at stations with a larger dip. However, complicated
                  dependences on solar activity can be found in the diurnal
                  mean and the semidiurnal phases of equivalent winds at
                  stations considered.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{lobzin2002,
  AUTHOR = {Lobzin, V.V. and Pavlov, A.V.},
  TITLE = {Solar zenith angle dependencies of F1-layer, NmF2 negative
                  disturbance, and G-condition occurrence probabilities},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2002},
  VOLUME = {20},
  NUMBER = {11},
  PAGES = {1821--1836},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {Experimental data acquired by the Ionospheric Digital
                  Database of the National Geophysical Data Center, Boulder,
                  Colorado, from 1957 to 1990, are used to study the
                  dependence of the G condition, F1-layer, and NmF2 negative
                  disturbance occurrence probabilities on the solar zenith
                  angle during summer, winter, spring, and autumn months in
                  latitude range 1 (between -10degrees and +10degrees of the
                  geomagnetic latitude, Phi), in latitude range 2 (10degrees <
                  \&UPhi;\ &LE; 30&DEG;), in latitude range 3 (30&DEG; < \phi\
                  less than or equal to 45degrees, 30degrees < \&UPhi;\ &LE;
                  45&DEG;), in latitude range 4 (45&DEG; < \ phi\ less than or
                  equal to 60degrees, 45degrees < \&UPhi;\ &LE; 60&DEG;), and
                  in latitude range 5 (60&DEG; < \Phi\ less than or equal to
                  90degrees), where phi is the geographic latitude. Our
                  calculations show that the G condition is more likely to
                  occur during the first half of a day than during the second
                  half of a day, at all latitudes during all seasons for the
                  same value of the solar zenith angle. The F1-layer
                  occurrence probability is larger in the first half of a day
                  in comparison with that in the second half of a day for the
                  same value of the solar zenith angle in latitude range I for
                  all seasons, while the F1-layer occurrence probability is
                  approximately the same for the same solar zenith angle
                  before and after noon in latitude ranges 4 and 5. The
                  F1-layer and G condition are more commonly formed near
                  midday than close to post sunrise or pre-sunset. The chance
                  that the daytime F1-layer and G condition will be formed is
                  greater in summer than in winter at the given solar zenith
                  angle in latitude ranges 2-5, while the F1-layer occurrence
                  probability is greater in winter than in summer for any
                  solar zenith angle in latitude range 1. The calculated
                  occurrence probability of the NmF2 weak negative
                  disturbances reaches its maximum and minimum values during
                  daytime and night-time conditions, respectively, and the
                  average night-time value of this probability is less than
                  that by day for all seasons in all studied latitude
                  regions. It is shown that the NmF2 normal, strong, and very
                  strong negative disturbances are more frequent on average at
                  night than by day in latitude ranges 1 and 2 for all
                  seasons, reaching their maximum and minimum occurrence
                  probability values at night and by day, respectively. This
                  conclusion is also correct for all other studied latitude
                  regions during winter months, except for the NmF2 normal and
                  strong negative disturbances in latitude range 5. A
                  difference in the dependence of the strong and very strong
                  NmF2 negative disturbance percentage occurrences on the
                  solar zenith angle is found between latitude ranges 1 and
                  2. Our results provide evidence that the daytime dependence
                  of the G condition occurrence probability on the solar
                  zenith angle is determined mainly by the dependence of the
                  F1-layer occurrence probability on the solar zenith angle in
                  the studied latitude regions for winter months, in latitude
                  range 2 for all seasons, and in latitude ranges 4 and 5 for
                  spring, summer, and autumn months. The solar zenith angle
                  trend in the probability of the G condition occurrence in
                  latitude range 3 arises in the main from the solar zenith
                  angle trend in the F1-layer occurrence probability. The
                  solar zenith angle trend in the probabilities of strong and
                  very strong NmF2 negative disturbances counteracts the
                  identified solar zenith angle trend in the probability of
                  the G condition occurrence.}
}

@ARTICLE{ma2003,
  AUTHOR = {Ma, R.P. and Xu, H.Y. and Liao, H.},
  TITLE = {The features and a possible mechanism of semiannual
                  variation in the peak electron density of the low latitude
                  F2 layer},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  VOLUME = {65},
  NUMBER = {1},
  PAGES = {47--57},
  YEAR = {2003},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {Ionospheric data observed in 30 stations located in 3
                  longitude sectors (East Asia/Australia Sector, Europe/Africa
                  Sector and America/East Pacific Ocean Sector) during
                  1974-1986 are used to analyse the characteristics of
                  semiannual variation in the peak electron density of F2
                  layer (NmF2). The results indicate that the semiannual
                  variation of NmF2 mainly presents in daytime. In nighttime,
                  except in the region of geomagnetic equator between the two
                  crests of ionospheric equatorial anomaly, NmF2 has no
                  obvious semiannual variation. In the high latitude region,
                  only in solar maxima years and in daytime, there are obvious
                  semiannual variations of NmF2. The amplitude distribution of
                  the semiannual variation of daytime NmF2 with latitude has a
                  "double-humped structure", which is very similar to the
                  ionospheric equatorial anomaly. There is asymmetry between
                  the Southern and the Northern Hemispheres of the profile of
                  the amplitude of semiannual variation of NmF2 and
                  longitudinal difference. A new possible mechanism of
                  semiannual variation of NmF2 is put forward in this
                  paper. The semiannual variation of the diurnal tide in the
                  lower thermosphere induces the semiannual variation of the
                  amplitude of the equatorial electrojet. This causes the
                  semiannual variation of the amplitude of ionospheric
                  equatorial anomaly through fountain effect. This process
                  induces the semiannual variation of the low latitude NmF2.}
}

@ARTICLE{mansilla2004:_mid_latitude,
  AUTHOR = {Mansilla, G.A.},
  TITLE = {Mid-latitude ionospheric effects of a great geomagnetic
                  storm},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2004},
  VOLUME = {66},
  NUMBER = {12},
  PAGES = {1085--1091},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {On March 13, 1989 magnetic storm effects on the mid- and
                  low-latitude ionosphere were investigated. For this, peak
                  electron density of 172-layer (NmF2) data from four chains
                  of ionospheric stations located in the geographic longitude
                  ranges 10degreesW-15degreesE, 55degreesE-85degreesE,
                  135degreesE-155degreesE and 200degreesE-255degreesE were
                  used. Relative deviations of perturbed NmF2 from their
                  respective quiet-time values were considered. Long-lasting
                  negative storm effects were the dominant characteristic
                  observed at middle latitudes, which occurred since the main
                  phase of the storm. In general, the most significant
                  negative disturbances were observed at middle-high
                  latitudes. In the longitudinal sectors in which the storm
                  started at day-time and pre-dusk hours, positive storm
                  effects at middle and low latitudes were observed during the
                  main phase. The role of some physical mechanisms to explain
                  the ionospheric effects is also considered.}
}

@ARTICLE{marin01:_long_euras,
  AUTHOR = {Marin, D. and Mikhailov, A.V. and de la Morena, B.A. and
                  Herraiz, M.},
  TITLE = {Long-term hmF2 trends in the Eurasion longitudinal sector
                  from the ground-based ionosonde observations},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2001},
  VOLUME = {19},
  PAGES = {761--772},
  ABSTRACT = {The method earlier used for the foF2 long-term trends
                  analysis is applied to reveal hmF2 long-term trends at 27
                  ionosonde stations in the European and Asian longitudinal
                  sectors. Observed M(3000)F2 data for the last 3 solar cycles
                  are used to derive hmF2 trends. The majority of the studied
                  stations show significant hmF2 linear trends with a
                  confidence level of at least 95\% for the period after 1965,
                  with most of these trends being positive. No systematic
                  variation of the trend magnitude with latitude is revealed,
                  but some longitudinal effect does take place. The proposed
                  geomagnetic storm concept to explain hmF2 long-term trends
                  proceeds from a natural origin of the trends rather than an
                  artificial one related to the thermosphere cooling due to
                  the greenhouse effect.},
  KEYWORDS = {Ionosphere (ionosphere-atmosphere interaction)},
  URL = {http://www.copernicus.org/EGU/annales/19/761.html},
  URL = {http://www.copernicus.org/EGU/annales/19/ag19/761.pdf},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{materassi2005,
  AUTHOR = {Materassi, M. and Mitchell, C.N.},
  TITLE = {A simulation study into constructing of the sample space for 
                  ionospheric imaging},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2005},
  VOLUME = {67},
  NUMBER = {12},
  PAGES = {1085--1091},
  ABSTRACT = {Ionospheric imaging usually involves solving an underdetermined inversion problem. The inversion is performed involving additional constraints to enforce realistic profiles in the vertical. One way to incorporate those vertical profile constraints is to perform the inversion using Empirical Orthogonal Functions (EOFs). The need of defining a sample space spanned by EOFs to obtain ionospheric images yields the possibility to employ ionosonde measurements in ionospheric tomography based on stochastic inversion of GPS data. Here we present a simulation study based on an existing network of GPS ground receivers and ionosondes across Europe. The locations of the transmitters used in the simulation are actual satellite positions. Simulated GPS data, constructed assuming that the ionosphere is the international reference ionosphere, are inverted via the Multi Instrument Data Analysis System. The sample space of this stochastic inversion is constructed employing ionosonde measurements simulated from the same model ionosphere. Such use of ionosonde data to construct the sample space produces better results than without ionosonde data.},
  KEYWORDS = {Electromagnetic methods; Ionosphere; Radio propagation; Remote sensing; Radio tomography; Data inversion},
  URL = {http://dx.doi.org/10.1016/j.jastp.2005.02.019},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {}
}

@ARTICLE{mendillo2002,
  AUTHOR = {Mendillo, A. and Rishbeth, H. and Roble, R.G. and Wroten,
                  J.},
  TITLE = {Modelling F2-layer seasonal trends and day-to-day
                  variability driven by coupling with the lower atmosphere},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2002},
  VOLUME = {64},
  NUMBER = {18},
  PAGES = {1911--1931},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  ABSTRACT = {This paper presents results from the TIME-GCM-CCM3
                  thermosphere-ionosphere-lower atmosphere flux-coupled model,
                  and investigates how well the model simulates known F2-layer
                  day/night and seasonal behaviour and patterns of day-to-day
                  variability at seven ionosonde stations. Of the many
                  possible contributors to F2-layer variability, the present
                  work includes only the influence of 'meteorological'
                  disturbances transmitted from lower levels in the
                  atmosphere, solar and geomagnetic conditions being held at
                  constant levels throughout a model year. In comparison to
                  ionosonde data, TIME-GCM-CCM3 models the peak electron
                  density (NmF2) quite well, except for overemphasizing the
                  daytime summer/winter anomaly in both hemispheres and
                  seriously underestimating night NmF2 in summer. The peak
                  height hmF2 is satisfactorily modelled by day, except that
                  the model does not reproduce its observed semiannual
                  variation. Nighttime values of hmF2 are much too low, thus
                  causing low model values of night NmF2. Comparison of the
                  variations of NmF2 and the neutral [O/N-2] ratio supports
                  the idea that both annual and semiannual variations of
                  F2-layer electron density are largely caused by changes of
                  neutral composition, which in turn are driven by the global
                  thermospheric circulation. Finally, the paper describes and
                  discusses the characteristics of the F2-layer response to
                  the imposed 'meteorological' disturbances. The ionospheric
                  response is evaluated as the standard deviations of five
                  ionospheric parameters for each station within 11-day blocks
                  of data. At any one station, the patterns of variability
                  show some coherence between different parameters, such as
                  peak electron density and the neutral atomic/molecular
                  ratio. Coherence between stations is found only between the
                  closest pairs, some 2500 km apart, which is presumably
                  related to the scale size of the 'meteorological'
                  disturbances. The F2-layer day-to-day variability appears to
                  be related more to variations in winds than to variations of
                  thermospheric composition.}
}

@ARTICLE{mikhailov01,
  AUTHOR = {Mikhailov, A.V. and Marin, D.},
  TITLE = {An interpretation of the foF2 and hmF2 long-term trends in
                  the framework of the geomagnetic control concept},
  JOURNAL = {Annales Geophysicae},
  PAGES = {733-748},
  YEAR = {2001},
  VOLUME = {17},
  NUMBER = {7},
  ABSTRACT = {Earlier revealed morphological features of the foF2 and hmF2
                  long-term trends are interpreted in the scope of the
                  geomagnetic control concept based on the contemporary
                  F2-layer storm mechanisms. The F2-layer parameter trends
                  strongly depend on the long-term varying geomagnetic
                  activity whose effects cannot be removed from the trends
                  using conventional indices of geomagnetic
                  activity. Therefore, any interpretation of the foF2 and hmF2
                  trends should consider the geomagnetic effects as an
                  inalienable part of the trend analysis. Periods with
                  negative and positive foF2 and hmF2 trends correspond to the
                  periods of increasing or decreasing geomagnetic activity
                  with the turning points around 1955, and the end of 1960s
                  and 1980s, where foF2 and hmF2 trends change their
                  signs. Such variations can be explained by neutral
                  composition, as well as temperature and thermospheric wind
                  changes related to geomagnetic activity variations. In
                  particular, for the period of increasing geomagnetic
                  activity (1965-1991) positive at lower latitudes, but
                  negative at middle and high latitudes, foF2 trends may be
                  explained by neutral composition and temperature changes,
                  while soft electron precipitation determines nighttime
                  trends at sub-auroral and auroral latitudes. A pronounced
                  dependence of the foF2 trends on geomagnetic (invariant)
                  latitude and the absence of any latitudinal dependence for
                  the hmF2 trends are due to different dependencies of NmF2
                  and hmF2 on main aeronomic parameters. All of the revealed
                  latitudinal and diurnal foF2 and hmF2 trend variations may
                  be explained in the frame-work of contemporary F2-region
                  storm mechanisms. The newly proposed geomagnetic storm
                  concept used to explain F2-layer parameter long-term trends
                  proceeds from a natural origin of the trends rather than an
                  artificial one, related to the thermosphere cooling due to
                  the greenhouse effect. Within this concept, instead of
                  cooling, one should expect the thermosphere heating for the
                  period of increasing geomagnetic activity (1965-1991).},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{mikhailov2000,
  AUTHOR = {Mikhailov, A.V. and Marin, D.},
  TITLE = {Geomagnetic control of the foF2 long-term trends},
  JOURNAL = {Annales Geophysicae},
  YEAR = {2000},
  VOLUME = {18},
  NUMBER = {6},
  PAGES = {653--665},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {Further development of the method proposed by Danilov and
                  Mikhailov is presented. The method is applied to reveal the
                  foF2 long-term trends on 30 Northern Hemisphere ionosonde
                  stations. Most of them show significant foF2 trends. A
                  pronounced dependence of trend magnitude on geomagnetic
                  (invariant) latitude is confirmed. Periods of
                  negative/positive foF2 trends corresponding to the periods
                  of long-term increasing/ decreasing geomagnetic activity are
                  revealed for the first time. Pronounced diurnal variations
                  of the foF2 trend magnitude are found. Strong positive foF2
                  trends in the post-midnight-early-morning LT sector and
                  strong negative trends during daytime hours are found on the
                  sub-auroral stations for the period with increasing
                  geomagnetic activity. On the contrary middle and lower
                  latitude stations demonstrate negative trends in the
                  early-morning LT sector and small negative or positive
                  trends during daytime hours for the same period. All the
                  morphological features revealed of the foF2 trends may be
                  explained in the framework of contemporary F2-region storm
                  mechanisms. This newly proposed F2-layer geomagnetic storm
                  concept casts serious doubts on the hypothesis relating the
                  F2-layer parameter long-term trends to the thermosphere
                  cooling due to the greenhouse effect.}
}

@ARTICLE{mikhailov01b,
  AUTHOR = {Mikhailov, A.V. and Marin, D. and Leschinskaya, T.Yu. and
                  Herraiz, M.},
  TITLE = {A revised approach to the foF2 long-term trends analysis},
  JOURNAL = {Annales Geophysicae},
  PAGES = {1663-1675},
  YEAR = {2002},
  VOLUME = {20},
  ABSTRACT = {A new approach to extract foF2 long-term trends, which are
                  free to a great extent from solar and geomagnetic activity
                  effects, has been proposed. These trends are insensitive to
                  the phase (increasing/decreasing) of geomagnetic activity,
                  with long-term variations being small and insignificant for
                  such relatively short time periods. A small but significant
                  residual foF2 trend, with the slope Kr = - 2.2  10-4
                  per year, was obtained over a 55-year period (the longest
                  avail-able) of observations at Slough. Such small trends
                  have no practical importance. On the other hand, negative
                  (although insignificant) residual trends obtained at 10
                  ionosonde stations for shorter periods (31 years) may be
                  considered as a manifestation of a very long-term
                  geomagnetic activity increase which did take place during
                  the 20th century. All of the revealed foF2 long-term
                  variations (trends) are shown to have a natural origin
                  related to long-term variations in solar and geomagnetic
                  activity. There is no indication of any manmade foF2
                  trends.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{minnis1955,
  AUTHOR = {Minnis, C.M.},
  TITLE = {A new index of solar activity based on ionospheric
                  measurements},
  JOURNAL = {Journal of Atmospheric and Terrestrial Physics},
  PAGES = {310--321},
  YEAR = {1955},
  VOLUME = {7},
  ABSTRACT = {The monthly mean relative sunspot number (RM) is assumed to
                  contain a component (Rv) which has a one-to-one correlation
                  with the critical frequency of the F2-layer in an
                  undisturbed ionosphere and which is, therefore, an idealized
                  index of solar activity. The residual component (Rx) may be
                  regarded as an error which has a Standard Deviation of about
                  20 per cent. A new index (IF2) has been constructed for the
                  period 1938%G–%@1954; like RM, it can
                  also be regarded as giving an approximate value of Rv, but
                  its residual error component (Rz) has an S.D. which is only
                  about one tenth that of Rx. The magnitude of IF2, for a
                  given month is computed from the mean noon critical
                  frequencies in the F2-layer at Slough, Huancayo, and
                  Watheroo, which are normally available within a few weeks of
                  the end of each month. The index is based, in effect, on a
                  calibration of the F2-layer critical frequencies at these
                  observatories in terms of Rv, using data extending back as
                  far as possible. Precautions have been taken to reduce to
                  negligible proportions the effects of ionospheric
                  disturbances on the magnitude of the new index.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{minnis1960,
  AUTHOR = {Minnis, C.M. and Bazzard, G.H.},
  TITLE = {A monthly ionospheric index of solar activity based on
                  F2-layer ionization at eleven stations},
  JOURNAL = {Journal of Atmospheric and Terrestrial Physics},
  PAGES = {297--305},
  YEAR = {1960},
  VOLUME = {18},
  NUMBER = {4},
  ABSTRACT = {A monthly index has been constructed, for the period 1938 to
                  date, using monthly mean or median noon values of foF2 at
                  eleven widely-distributed stations. The correlation between
                  foF2 at noon and this index is significantly greater than
                  that between foF2 and either the 3 month weighted mean
                  sunspot number or the monthly mean solar radio noise flux at
                  2800 Mc/s. Numerical estimates have been made of the errors
                  incurred in forecasting noon and midnight foF2 several
                  months ahead using these three indices as guides to the
                  trend of solar activity.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{muhtarov01:_europ,
  AUTHOR = {Muhtarov, P. and Kutiev I. and Cander, L.R. and Zolesi, B. and de Franceschi, G. and Levy, M. and Dick, M.},
  TITLE = {European ionospheric forecast and mapping},
  JOURNAL = {Physics and Chemistry of the earth part C-Solar-Terrestial and Planetary Science},
  YEAR = 2001,
  VOLUME = 26,
  NUMBER = 5,
  PAGES = {347--351},
  ABSTRACT = {A new technique is developed for forecasting and instantaneous
              mapping of the ionospheric parameters over Europe, based on
              analytical presentation of the mapped quantities. The diurnal
              and seasonal variations of the ionospheric foF2 and M(3000)F2
              parameters are represented by a modified version of the regional
              model ISIRM adjusted to the past measured data. An
              autoregressive extrapolation of the data from the past month
              enables the 15-day-ahead forecast of the quiet ionospheric
              distribution to be performed. In addition, the short-term
              variations due to geomagnetic activity are defined as a plane
              surface superimposed on the quiet distribution. This correction
              is obtained by two plane characteristics as functions of the
              geomagnetic three-hour Kp index. In this way the 24-hour
              forecast can be obtain during quiet as well as disturbed
              ionospheric conditions. The corresponding EIFM software provides
              a variety of options to perform the short-term forecast
              depending on availability of the measured ionospheric data and
              predicted Kp values.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {}
}

@ARTICLE{oliveros2005,
  AUTHOR = {Oliveros, B.M. and Hernandez R.D.M. and Saurez L.P.},
  TITLE = {On the onset and meridional propagation of the ionospheric 
                  F2-region response to geomagnetic storms},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2005},
  VOLUME = {67},
  NUMBER = {17--18},
  PAGES = {1706--1714},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1016/j.jastp.2004.12.013},
  ABSTRACT = {The meridional propagation velocities of the ionospheric 
                  F2-region response to 268 geomagnetic storms are calculated. 
                  Ionospheric vertical sounding data of I h time resolution 
                  from several stations located in a longitude sector 
                  approximately centred along the great circle that contains 
                  both the geomagnetic poles and the geographic poles are used.

                  Most meridional propagation velocities from high to low 
                  latitudes are less than 600 m/s. The smaller velocities are 
                  typical of global neutral meridional wind circulation and the
                  larger are representative of traveling atmospheric 
                  disturbances.

                  Simultaneous disturbances at several locations are more 
                  frequent during positive phases than during negative phases. 
                  Negative phase meridional propagation velocities associated 
                  with meridional neutral winds are less frequent in the 
                  southern hemisphere when compared with corresponding 
                  velocities observed in the northern hemisphere. This may be 
                  related to the fact that the distance between the geomagnetic
                  pole and the equator is smaller in the northern hemisphere.

                  Most negative phase onsets are within the 06-10 LT interval. 
                  For middle geomagnetic latitudes a "forbidden time interval" 
                  between 11 and 14 LT is present. The positive phase onsets 
                  show the "dusk effect". (c) 2005 Elsevier Ltd. All rights 
                  reserved.}
}

@ARTICLE{ozguc98:_examin,
  AUTHOR = {Ozguc, A. and Tulunay, Y. and Atac, T.},
  TITLE = {Examination of the solar cycle variation of foF2 by using
                  solar flare index for the cycle 21},
  JOURNAL = {Advances in Space Research},
  PAGES = {139--142},
  YEAR = {1998},
  MONTH = {jan},
  VOLUME = {22},
  NUMBER = {1},
  ABSTRACT = {For solar cycle 21 (1976 - 1986) the variation of monthly
                  mean values of noon-time foF2 at Slough, Rome, and Manila
                  are examined by using solar flare index and geomagnetic Ap
                  index. A single regression analysis for dependence of foF2
                  on solar flare index shows better matching. Moreover, less
                  hysteresis effect is seen when we use solar flare index
                  instead of other solar indices. Thus, for making prediction,
                  one needs to take into account just the solar flare index
                  and not the solar flare index and geomagnetic Ap index
                  simultaneously.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{peitrella05,
  AUTHOR = {Pietrella, M. and Perrone, L.},
  TITLE = {Instantaneous space-weighted ionospheric regional model for
                  instantaneous mapping of the critical frequency of the F2
                  layer in the European region},
  JOURNAL = {Radio Science},
  YEAR = {2005},
  VOLUME = {40},
  NUMBER = {1},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1029/2003RS003008},
  ABSTRACT = {An instantaneous space-weighted ionospheric regional model
                  (ISWIRM) for the regional now-casting of the critical
                  frequency of the F2 layer ( foF2) has been developed. The
                  geographical area of applicability of the model is ranged
                  between 35degreesN - 70degreesN and 5degreesW -
                  40degreesE. Inside this region the hourly values of foF2 are
                  obtained, correcting the monthly medians values of foF2
                  predicted by the space-weighted ionospheric local model (
                  SWILM) on the basis of hourly observations of foF2 coming
                  from four reference stations ( Rome, Chilton, Lycksele, and
                  Loparskaya ( or Sodankyla)). The performance of the model,
                  evaluated at four testing stations ( Tortosa, Juliusruh,
                  Uppsala, and Kiruna) during some periods characterized by
                  strong solar and geomagnetic activity, can be considered
                  satisfactory, given that the hourly values of the residuals
                  are almost always below 1 MHz. A comparison between ISWIRM's
                  performance using manually validated and autoscaled data of
                  foF2 and SWILM's performance was made for two disturbed
                  periods. One example of instantaneous ionospheric mapping of
                  foF2 relative to the selected disturbed periods is also
                  shown.}
}

@ARTICLE{reinisch04:automated_ionospheric_digisonde_network,
  AUTHOR = {Reinisch, B.W. and Galkin, I.A. and Khmyrov, G. and Kozlov,
                  A. and Kitrosser, D.F.},
  TITLE = {Automated collection and dissemination of ionospheric data
                  from the digisonde network},
  JOURNAL = {Advances in Space Research},
  YEAR = 2004,
  VOLUME = 2,
  PAGES = {241--247},
  ABSTRACT = {The growing demand for fast access to accurate ionospheric
                  electron density profiles and ionospheric characteristics
                  calls for efficient dissemination of data from the many
                  ionosondes operating around the globe. The global digisonde
                  network with over 70 stations takes advantage of the
                  Internet to make many of these sounders remotely accessible
                  for data transfer and control. Key elements of the digisonde
                  system data management are the visualization and editing
                  tool SAO Explorer, the digital ionogram database DIDBase,
                  holding raw and derived digisonde data under an
                  industrial-strength database management system, and the
                  automated data request execution system ADRES.},
  URL = {http://www.copernicus.org/URSI/ars/ARS_2_1/241.pdf},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{rishbeth01:_patterns_f2_variability,
  AUTHOR = {Rishbeth, H. and Mendillo, M.},
  TITLE = {Patterns of F2-layer variability},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  YEAR = {2001},
  VOLUME = {63},
  NUMBER = {15},
  PAGES = {1661--1680},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  ABSTRACT = {The ionosphere displays variations on a wide range of
                  time-scales, ranging from operational time-scales of hours
                  and days up to solar cycles and longer. We use ionosonde
                  data from thirteen stations to study the day-to-day
                  variability of the peak F2-layer electron density, NmF2,
                  which we use to define quantitative descriptions of
                  variability versus local time, season and solar cycle. On
                  average, for years of medium solar activity (solar
                  decimetric flux approximately 140 units), the daily
                  fluctuations of NmF2 have a standard deviation of 20% by
                  day, and 33% by night. We examine and discuss the patterns
                  of behaviour of ionospheric and geomagnetic variability, in
                  particular the equinoctial peaks. For further analysis we
                  concentrate on one typical midlatitude station, Slough. We
                  find that the standard deviations of day-to-day and
                  night-to-night values of Slough NmF2 at first increase with
                  increasing length of the dataset, become fairly constant at
                  lengths of 10-20 days and then increase further (especially
                  at equinox) because of seasonal changes. We found some
                  evidence of two-day waves, but they do not appear to be a
                  major feature of Slough's F2 layer. Putting together the
                  geomagnetic and ionospheric data, and taking account of the
                  day-to-day variability of solar and geomagnetic parameters,
                  we find that a large part of F2-layer variability is linked
                  to that of geomagnetic activity, and attribute the rest to
                  'meteorological' sources at lower levels in the
                  atmosphere. We suggest that the greater variability at night
                  is due to enhanced auroral energy input, and to the lack of
                  the strong photochemical control of the F2-layer that exists
                  by day.}
}

@ARTICLE{rishbeth04,
  AUTHOR = {Rishbeth, H. and Mendillo, M.},
  TITLE = {Ionospheric layers of Mars and Earth},
  JOURNAL = {Planetary and Space Science},
  PAGES = {849-852},
  YEAR = {2004},
  MONTH = {aug},
  VOLUME = {52},
  NUMBER = {9},
  URL = {http://dx.doi.org/10.1016/j.pss.2004.02.007},
  ABSTRACT = {We compare the electron densities of two martian ionospheric
                  layers, which we call M1 and M2, measured by Mars Global
                  Surveyor during 9-27 March 1999, with the electron densities
                  of the terrestrial E and F1 layers derived from ionosonde
                  data at six sites. The day-to-day variations are all linked
                  to changes in solar activity, and provide the opportunity of
                  making the first simultaneous study of four photochemical
                  layers in the solar system. The `ionospheric layer index',
                  which we introduce to characterize ionospheric layers in
                  general, varies between layers because different atmospheric
                  chemistry and solar radiations are involved. The M2 and F1
                  layer peaks occur at similar atmospheric pressure levels,
                  and the same applies to the M1 and E layers.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}

@ARTICLE{rishbeth00_semiann,
  AUTHOR = {Rishbeth, H. and Sedgemore-Schulthess, K.J.F. and Ulich, T.},
  TITLE = {Semiannual and annual variations in the height of the
                  ionospheric F2-peak},
  JOURNAL = {Annales Geophysicae},
  PAGES = {285--299},
  YEAR = {2000},
  VOLUME = {18},
  NUMBER = {3},
  ABSTRACT = {Ionosonde data from sixteen stations are used to study the
                  semiannual and annual variations in the height of the
                  ionospheric F2-peak, hmF2. The semiannual variation, which
                  peaks shortly after equinox, has an amplitude of about 8 km
                  at an average level of solar activity (10.7 cm flux = 140
                  units), both at noon and midnight. The annual variation has
                  an amplitude of about 11 km at northern midlatitudes,
                  peaking in early summer; and is larger at southern stations,
                  where it peaks in late summer. Both annual and semiannual
                  amplitudes increase with increasing solar activity by day,
                  but not at night. The semiannual variation in hmF2 is
                  unrelated to the semiannual variation of the peak electron
                  density NmF2, and is not reproduced by the CTIP and TIME-GCM
                  computational models of the quiet-day thermosphere and
                  ionosphere. The semiannual variation in hmF2 is
                  approximately "isobaric", in that its amplitude corresponds
                  quite well to the semiannual variation in the height of
                  fixed pressure-levels in the thermosphere, as represented by
                  the MSIS empirical model. The annual variation is not
                  "isobaric". The annual mean of hmF2 increases with solar
                  10.7 cm flux, both by night and by day, on average by about
                  0.45 km/flux unit, rather smaller than the corresponding
                  increase of height of constant pressure-levels in the MSIS
                  model. The discrepancy may be due to solar-cycle variations
                  of thermospheric winds. Although geomagnetic activity, which
                  affects thermospheric density and temperature and therefore
                  hmF2 also, is greatest at the equinoxes, this seems to
                  account for less than half the semiannual variation of
                  hmF2. The rest may be due to a semiannual variation of tidal
                  and wave energy transmitted to the thermosphere from lower
                  levels in the atmosphere.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}

@ARTICLE{schunk04,
  AUTHOR = {Schunk, R. W. and Scherliess, L. and Sojka, J. J. and
                  Thompson, D. C. and Anderson, D. N. and Codrescu, M. and
                  Minter, C. and Fuller-Rowell, T. J. and Heelis, R. A. and
                  Hairston, M. and Howe, B. M.},
  TITLE = {Global Assimilation of Ionospheric Measurements (GAIM)},
  JOURNAL = {Radio Science},
  YEAR = {2004},
  VOLUME = {39},
  ABSTRACT = {The ionosphere is a highly dynamic medium that exhibits
                  weather disturbances at all latitudes, longitudes, and
                  altitudes, and these disturbances can have detrimental
                  effects on both military and civilian systems. In an effort
                  to mitigate the adverse effects, we are developing a
                  physics-based data assimilation model of the ionosphere and
                  neutral atmosphere called the Global Assimilation of
                  Ionospheric Measurements (GAIM). GAIM will use a
                  physics-based ionosphere-plasmasphere model and a Kalman
                  filter as a basis for assimilating a diverse set of
                  real-time (or near real-time) measurements. Some of the data
                  to be assimilated include in situ density measurements from
                  satellites, ionosonde electron density profiles, occultation
                  data, ground-based GPS total electron contents (TECs),
                  two-dimensional ionospheric density distributions from
                  tomography chains, and line-of-sight UV emissions from
                  selected satellites. When completed, GAIM will provide
                  specifications and forecasts on a spatial grid that can be
                  global, regional, or local. The primary output of GAIM will
                  be a continuous reconstruction of the three-dimensional
                  electron density distribution from 90 km to geosynchronous
                  altitude (35,000 km). GAIM also outputs auxiliary
                  parameters, including N m F 2, h m F 2, NmE, hmE, and slant
                  and vertical TEC. Furthermore, GAIM provides global
                  distributions for the ionospheric drivers (neutral winds and
                  densities, magnetospheric and equatorial electric fields,
                  and electron precipitation patterns). In its specification
                  mode, GAIM yields quantitative estimates for the accuracy of
                  the reconstructed ionospheric densities.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1029/2002RS002794}
}

@ARTICLE{sethi2002,
  AUTHOR = {Sethi, N.K. and Goel, M.K. and Mahajan, K.K.},
  TITLE = {Solar Cycle variations of foF2 from IGY to 1990},
  JOURNAL = {Annales Geophysicae},
  VOLUME = {20},
  NUMBER = {10},
  YEAR = {2002},
  PAGES = {1677--1685},
  UKSSDC_D = {},
  UKSSDC_I = {},
  ABSTRACT = {Noontime monthly median values of F2-layer critical
                  frequency foF2 (m) for some ionospheric stations
                  representing low- and mid-latitudes are examined for their
                  dependence on solar activity for the years 1957 (IGY) to
                  1990. This is the period for which ionospheric data in
                  digital form is available in two CD-ROMs at the World Data
                  Center, Boulder. It is observed that at mid-latitudes, foF2
                  (m) shows nearly a linear relationship with R12 (the
                  12-month running average of the Zurich sunspot number),
                  though this relation is nonlinear for low-latitudes. These
                  results indicate some departures from the existing
                  information often used in theoretical and applied areas of
                  space research.}
}

@ARTICLE{stamper98:_solar_causes_long_term_increas_geomag_activ,
  AUTHOR = {Stamper, R. and Lockwood, M. and Wild, M.N. and Clark,
                  T.D.G.},
  TITLE = {Solar Causes of the Long-Term Increase in Geomagnetic
                  Activity},
  JOURNAL = {Journal of Geophysical Research},
  PAGES = {28325--28342},
  YEAR = {1999},
  MONTH = DEC,
  VOLUME = {104},
  NUMBER = {A12},
  UKSSDC_W = {},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {},
  ABSTRACT = {We analyze the causes of the century-long increase in
                  geomagnetic activity, quantified by annual means of the {\it
                  aa} index, using observations of interplanetary space,
                  galactic cosmic rays, the ionosphere, and the auroral
                  electrojet, made during the last three solar cycles. The
                  effects of changes in ionospheric conductivity, the Earth's
                  dipole tilt, and magnetic moment are shown to be small; only
                  changes in near-Earth interplanetary space make a
                  significant contribution to the long-term increase in
                  activity. We study the effects of the interplanetary medium
                  by applying dimensional analysis to generate the optimum
                  solar wind-magnetosphere energy coupling function, having an
                  unprecedentedly high correlation coefficient of
                  0.97. Analysis of the terms of the coupling function shows
                  that the largest contributions to the drift in activity over
                  solar cycles 20--22 originate from rises in the average
                  interplanetary magnetic field (IMF) strength, solar wind
                  concentration, and speed; average IMF orientation has grown
                  somewhat less propitious for causing geomagnetic
                  activity. The combination of these factors explains almost
                  all of the 39\% rise in {\it aa} observed over the last
                  three solar cycles. Whereas the IMF strength varies
                  approximately in phase with sunspot numbers, neither its
                  orientation nor the solar wind density shows any coherent
                  solar cycle variation. The solar wind speed peaks strongly
                  in the declining phase of even-numbered cycles and can be
                  identified as the chief cause of the phase shift between the
                  sunspot numbers and the {\it aa} index. The rise in the IMF
                  magnitude, the largest single contributor to the drift in
                  geomagnetic activity, is shown to be caused by a rise in the
                  solar coronal magnetic field, consistent with a rise in the
                  coronal source field, modeled from photospheric
                  observations, and an observed decay in cosmic ray fluxes.}
}

@ARTICLE{stanislawska2001:_generation,
  AUTHOR = {Stanislawska, I. and Juchnikowski, G. and Zbyszynski, Z},
  TITLE = {Generation of instantaneous, maps of ionospheric
                  characteristics},
  JOURNAL = {Radio Science},
  YEAR = {2001},
  VOLUME = {36},
  NUMBER = {5},
  PAGES = {1073--1081},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1029/1999RS002289},
  ABSTRACT = {A way of producing limited-area instantaneous maps of
                  ionospheric characteristics is shown. An interpolation
                  technique is applied for construction of the mapping
                  model. The model combines monthly median maps of ionospheric
                  characteristics and a set of measurements for a single
                  moment of time that are exactly replicated during the
                  mapping procedure. The accuracy of the mapping results is
                  discussed, and samples of maps for different geophysical
                  conditions for f(0)F(2), f(0)F(1), f(0)E and M(3000)F-2 are
                  presented.}
}

@ARTICLE{stanislawska2001:_forecasting,
  AUTHOR = {Stanislawska, I. and Zbyszynski, Z.},
  TITLE = {Forecasting of the ionospheric quiet and disturbed f(o)F(2)
                  values at a single location},
  JOURNAL = {Radio Science},
  YEAR = {2001},
  VOLUME = {36},
  NUMBER = {5},
  PAGES = {1065--1071},
  UKSSDC_D = {},
  UKSSDC_I = {},
  URL = {http://dx.doi.org/10.1029/1999RS002242},
  ABSTRACT = {The autocovariance prediction method has been used for
                  ionospheric forecasting of f(o)F(2) values for 1, 2, 4, 8,
                  and 12 hours ahead at a single location. Time series of
                  f(o)F(2) data for ionospheric quiet and disturbed conditions
                  for February 1986 and September and December 1990 at
                  different European stations were studied in order to clarify
                  the forecasting capabilities of the method for ionospheric
                  purposes. The accuracy of the method varies within
                  reasonable limits depending on the time range of the
                  forecast for different conditions. Samples of the results
                  for representative periods are presented. The forecast is
                  compared with observations, monthly median recommendations
                  of the Radiocommunication Sector of the International
                  Telecommunication Union (ITU-R), and persistence models.}
}

@ARTICLE{szuszczewicz1997,
  AUTHOR = {Szuszczewicz, E.P. and Blanchard, P. and Wilkinson, P. and
                  Crowley, G. and Fuller-Rowell, T. and Richards, P. and Abdu,
                  M. and Bullett, T. and Hanbaba, R. and Lebreton, J.P. and
                  Lester, M. and Lockwood, M. and Millward, G. and Wild,
                  M. and Pulinets, S. and Reddy, B.M. and Stanislawska, I. and
                  Vannaroni, G. and Zolesi, B.},
  TITLE = {The First Realtime Worldwide Ionospheric Prediction Network:
                  An Advance in Support of Spaceborne Experimentation, On-Line
                  Model Validation, and Space Weather},
  JOURNAL = {Geophysical Research Letters},
  PAGES = {449-452},
  YEAR = {1998},
  MONTH = {feb},
  VOLUME = {25},
  NUMBER = {4},
  ABSTRACT = {We report on the first realtime ionospheric predictions
                  network and its capabilities to ingest a global database and
                  forecast F-layer characteristics and ``in situ'' electron
                  densities along the track of an orbiting spacecraft. A
                  global network of ionosonde stations reported
                  around-the-clock observations of F-region heights and
                  densities, and an on-line library of models provided
                  forecasting capabilities. Each model was tested against the
                  incoming data; relative accuracies were intercompared to
                  determine the best overall fit to the prevailing conditions;
                  and the best-fit model was used to predict ionospheric
                  conditions on an orbit-to-orbit basis for the 12-hour period
                  following a twice-daily model test and validation
                  procedure. It was found that the best-fit model often
                  provided averaged (i.e., climatologically-based) accuracies
                  better than 5% in predicting the heights and critical
                  frequencies of the F-region peaks in the latitudinal domain
                  of the TSS-1R flight path. There was a sharp contrast,
                  however, in model-measurement comparisons involving
                  predictions of actual, unaveraged, along-track densities at
                  the 295 km orbital altitude of TSS-1R. In this case, extrema
                  in the first-principle models varied by as much as an order
                  of magnitude in density predictions, and the best-fit models
                  were found to disagree with the ``in situ'' observations of
                  Ne by as much as 140%. The discrepancies are interpreted as
                  a manifestation of difficulties in accurately and
                  self-consistently modeling the external controls of solar
                  and magnetospheric inputs and the spatial and temporal
                  variabilities in electric fields, thermospheric winds,
                  plasmaspheric fluxes, and chemistry.},
  UKSSDC_W = {},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {}
}

@ARTICLE{szuszczewicz92:_model,
  AUTHOR = {Szuszczewicz, E.P. and Fejer, B. and Roelof, E. and Schunk,
                  R. and Wolf, R. and Abdu, M. and Bateman, T. and Blanchard,
                  P. and Emery, B.A. and Feldstein, A. and Hanbaba, R. and
                  Joselyn, J. and Kikuchi, T. and Leitinger, R. and Lester,
                  M. and Sobral, J. and Reddy, B.M. and Richmond, A.D. and
                  Sica, R. and Walker, G.O. and Wilkinson, P.J.},
  TITLE = {Modelling and measurement of global-scale ionospheric
                  behaviour under solar minimum, equinoctial conditions},
  JOURNAL = {Advances in Space Research},
  PAGES = {105-115},
  YEAR = {1992},
  MONTH = {jan},
  VOLUME = {12},
  NUMBER = {6},
  ABSTRACT = {The global-scale modeling and measurement activities of the
                  Sundial campaign of September 1986 are examined, and
                  averaged, quiet-time, and dynamic ionospheric behaviors are
                  investigated. Treatment is given to developments in
                  empirical and first-principle models; and various aspects of
                  magnetospheric-thermospheric-ionospheric coupling mechanisms
                  are investigated. Overall results point to good empirical
                  model specification of averaged F-region behavior, with
                  suggestions for improvements in specification of layer peak
                  densities near and across the sunset terminator. The
                  difficulties in achieving a unique determination of electric
                  fields, thermospheric winds, and plasmaspheric fluxes are
                  elucidated in first-principle model attempts to reproduce
                  global observations of quiet-time F-region heights and
                  densities. In this connection, and in the treatment of
                  magnetospherically-imposed electric field influences on
                  low-latitude F-region dynamics, a greater need is shown for
                  comprehensive measurements of auroral oval dynamics,
                  thermospheric winds, electric fields, ion composition, and
                  ionospheric layer heights and densities. The growing
                  importance of the lower regions of the ionosphere and
                  thermosphere and the associated controls of dynamo-driven
                  electric fields are discussed.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {}
}

@ARTICLE{szuszczewicz88:_sundial,
  AUTHOR = {Szuszczewicz, E.P. and Fejer, B. and Roelof, E. and Schunk,
                  R. and Wolf, R. and Leitinger, R. and Abdu, M. and Reddy,
                  B.M. and Joselyn, J. and Wilkinson, P.J. and Woodman, R.},
  TITLE = {SUNDIAL: a world-wide study of interactive ionospheric
                  processes and their roles in the transfer of energy and mass
                  in the Sun-Earth system},
  JOURNAL = {Annales Geophysicae},
  PAGES = {3-18},
  YEAR = {1988},
  MONTH = {feb},
  VOLUME = {6},
  ABSTRACT = {Solar-terrestrial observations have been obtained in the
                  SUNDIAL program during the October 5-13, 1984 period in
                  order to explore cause and effect relationships controlling
                  the global-scale ionosphere. It is suggested that the
                  increased solar wind velocities noted are the result of a
                  corotating high-speed stream coupled to a transequatorial
                  solar coronal hole. The results are consistent with a
                  step-wise coupling of processes from the coronal hole
                  through the interplanetary and magnetospheric domains down
                  to the equatorial ionosphere, where penetrating electric
                  fields help trigger the most disturbed condition of
                  equatorial spread-F.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{szuszczewicz90:_solar_sundial,
  AUTHOR = {Szuszczewicz, E.P. and Wilkinson, P.J. and Abdu, M.A. and
                  Roelof, E. and Hanbaba, R. and Sands, M. and Kikuchi, T. and
                  Joselyn, J. and Burnside, R. and Lester, M. and Leitinger,
                  R. and Walker, G.O. and Reddy, B.M. and Sobral, J.},
  TITLE = {Solar-terrestrial conditions during Sundial-86 and empirical
                  modelling of the global-scale ionospheric response},
  JOURNAL = {Annales Geophysicae},
  PAGES = {387-398},
  YEAR = {1990},
  MONTH = {jun},
  VOLUME = {8},
  ABSTRACT = {Covering the period from September 22 through October 4,
                  1986, the Sundial-86 Solar-Minimum Equinoctial Campaign
                  studied the behavior of the global-scale ionosphere. The
                  period covered the most quiet (Q1) and second most disturbed
                  (D2) days of the entire month of September, with the
                  disturbed conditions triggered by a high-speed solar wind
                  stream. Ionospheric responses were monitored by the Sundial
                  network of nearly 70 stations distributed approximately in
                  three longitudinal domains; and global maps of f0F2 results
                  were compared with the 'predictions' of the International
                  Reference Ionosphere modified to include an empirical
                  specification of auroral oval boundaries and associated
                  high-latitude morphological domains. Comparisons that
                  included regions in the polar cap, diffuse auroral oval,
                  mid-latitude trough, equatorial anomaly, and the
                  sunrise/sunset terminator showed good agreement between the
                  hourly 8-day-averaged ionospheric observations and the
                  model.},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {}
}

@ARTICLE{szuszczewicz93:_measur_f_sundial,
  AUTHOR = {Szuszczewicz, E.P. and Wilkinson, P.J. and Swider, W. and
                  Pulinets, S. and Abdu, M.A. and Roelof, E. and
                  Fuller-Rowell, T. and Evans, D.S. and Bateman, T. and
                  Blanchard, P. and Gustafsson, G. and Hanbaba, R. and
                  Joselyn, J. and Kikuchi, T. and Leitinger, R. and Lester,
                  M. and Reddy, B.M. and Ruohoniemi, M. and Sands, M. and
                  Sobral, J. and Walker, G.O. and Wickwar, V.},
  TITLE = {Measurements and empirical model comparisons of F-region
                  characteristics and auroral oval boundaries during the
                  solstitial SUNDIAL campaign of 1987},
  JOURNAL = {Annales Geophysicae},
  PAGES = {601},
  YEAR = {1993},
  VOLUME = {11},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {}
}

@ARTICLE{tsagouri2005,
  AUTHOR = {Tsagouri, I. and Zolesi, B. and Belehaki, A. and 
                  Cander, Lj.},
  TITLE = {Evaluation of the performance of the real-time updated 
                  simplified ionospheric regional model for the European area},
  JOURNAL = {Journal of Atmospheric and Solar-Terrestrial Physics},
  VOLUME = {67},
  NUMBER = {12},
  PAGES = {1137--1146},
  YEAR = {2005},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {},
  ABSTRACT = {The increasing demand for upper-atmosphere nowcasting services for operational applications reveals the need for a realistic mapping of the ionosphere over Europe in real-time and especially during storm periods. To meet this need, a real-time updating method of simplified ionospheric regional model (SIRM) with autoscaled ionospheric characteristics observed by four European Digital Portable Sounders (DPS) ionosondes was recently developed. SIRM belongs to the group of ionospheric models for the standard vertical incidence (VI) ionospheric characteristics such as the critical frequency of the ionospheric F2 layer foF2 and the propagation factor M(3000)F2, which oversimplify a number of the ionospheric phenomena of real significance for radio communications applications showing satisfactory performance for median ionospheric condition description in restricted area of mid-latitudes. As a step forward, the rapid conversion of real-time data from four European digisondes to the driving parameters of the SIRM was introduced as the real-time SIRM updating (SIRMUP). In SIRMUP approach, the values of the ionospheric characteristics from first-guess model parameters at measurement points are combined with real-time measurements. The reliability of the real-time SIRM update method has already been tested in terms of the foF2 for various ionospheric conditions and the simulation results were very promising. In this paper, the simulation tests are continued in order to investigate the efficiency of the SIRMUP method in mapping the propagation conditions over Europe as they are expressed by the propagation factor M(3000)F2. In general, the results demonstrate that SIRMUP procedure has the potential to be used in real time for nowcasting the standard ionospheric characteristics over Europe, for operational applications.},
  KEYWORDS = {Ionospheric radio-propagation; Ionospheric mapping; Ionospheric modelling; Mid-latitude ionosphere},
  URL = {http://dx.doi.org/10.1016/j.jastp.2005.01.012}
}

@ARTICLE{tulunay1997:poss_eff_IMF_COST,
  AUTHOR = {Tulunay, Y. and Kaya, A. and Kaymaz, Z.},
  TITLE = {The Possible Effect of the IMF By and Bz Components on the
                  High Latitude COST 251 Area},
  JOURNAL = {Advances in Space Research},
  PAGES = {1723--1726},
  YEAR = {1997},
  VOLUME = {20},
  NUMBER = {9},
  ABSTRACT = {The possible effects of the orientation of the IMF on the
                  ionosphere has been studied by Tulunay (1995) using foF2
                  data from 15 ionospheric stations in Europe over the COST
                  238 area. The results showed that a good amount of the day
                  to day variability of the mid-latitude ionospheric F region
                  could be related to changes in orientation of the southward
                  IMF Bz. This variability is quantified as the maximum change
                  of deltafoF2. This paper investigates the effects of By
                  distribution on the ionospheric critical frequencies.},
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{variabilit:1995,
  AUTHOR = {Tulunay, Y.K.},
  TITLE = {Variability of mid-latitude ionospheric foF2 compared to IMF
                  polarity inversions},
  JOURNAL = {Advances in Space Research},
  PAGES = {35--44},
  YEAR = {1995},
  VOLUME = {15},
  NUMBER = {2},
  ABSTRACT = {Potential effects of the IMF-orientation on the mid-latitude
                  ionosphere are further investigated using critical
                  frequencies foF2 from six ionosonde stations. For a period
                  of 15 days around each inversion of BZ, excluding all days
                  with Ap >=6, a quiet standard diurnal variation was
                  determined by day-by-day averaging for each hour UT. The
                  regular diurnal, seasonal and solar cycle variations were
                  then removed from the data by substracting from these the
                  quiet standard value. The so obtained differences foF2 were
                  sorted after the IMF polarity. Distinct effects of northward
                  and southward inversions were found so that a large part of
                  the day-to day variability may be attributed to IMF BZ
                  polarity changes. },
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{wintoft2000,
  AUTHOR = {Wintoft, P. and Cander, L.R.},
  TITLE = {Twenty-four hour predictions of f(o)F(2) using time delay neural networks},
  JOURNAL = {Radio Science},
  YEAR = {2000},
  VOLUME = {35},
  NUMBER = {2},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {},
  ABSTRACT = {The use of time delay feed-forward neural networks to predict the hourly values of the ionospheric F-2 layer critical frequency, f(0)F(2), 24 hours ahead, have been examined. The 24 measurements of f(0)F(2) per day are reduced to five coefficients with principal component analysis. A time delay line of these coefficients is then used as input to a feed-forward neural network. Also included in the input are the 10.7 cm solar flux and the geomagnetic index Ap. The network is trained to predict measured f(0)F(2) data from 1965 to 1985 at Slough ionospheric station and validated on an independent validation set from the same station for the periods 1987-1990 and 1992-1994. The results are compared with two different autocorrelation methods for the years 1986 and 1991, which correspond to low and high solar activity, respectively.},
  KEYWORDS = {SOLAR-WIND DATA; GEOMAGNETIC STORMS},
  URL = {http://dx.doi.org/10.1029/1998RS002149}
}

@ARTICLE{wu95:_time_weigh,
  AUTHOR = {Wu, J.P. and Wilkinson, P.J.},
  TITLE = {Time Weighted magnetic indices as predictors of ionospheric
                  behaviour},
  JOURNAL = {Journal of Atmospheric and Terrestrial Physics},
  PAGES = {1763--1770},
  YEAR = {1995},
  VOLUME = {57},
  NUMBER = {14},
  ABSTRACT = {A time-weighted accumulation of the ap index, ap() (Wrenn,
                  1987; Wrenn et al., 1987, 1989), together with other similar
                  indices, was explored as a predictor of ionospheric
                  behaviour, using %Gƒ%@0F2 data for a selection of
                  locations in Australia and Europe for September and October
                  1989. All the time accumulated indices showed improved
                  linear correlations, indicative of a response time of the
                  order of about 15 hours. The response time could be
                  decomposed into a lag between respective time series and a
                  persistence time, although the decomposition appeared
                  unnecessary as the persistence time carried the same
                  information. Of the individual indices investigated, {\it
                  aa}() appeared best and the auroral oval equatorward edge
                  index (AI index) was poorest, although the differences were
                  not statistically significant. Comparisons between the {\it
                  aa}, ap and Kp indices, plus comparisons between different
                  ionospheric parameters showed that forecasting may be
                  improved using different transformations of the data. While
                  these results appear good, further studies using other
                  stations and seasons are warranted to confirm their utility
                  for forecasting. },
  UKSSDC_D = {},
  UKSSDC_I = {}
}

@ARTICLE{zolesi04:_real-time,
  AUTHOR = {Zolesi, B. and Belahaki, A. and Tsagouri, I. and Cander,
                  L.R.},
  TITLE = {Real-time updating of the Simplified Ionospheric Regional
                  Model for operational applications},
  JOURNAL = {Radio Science},
  YEAR = {2004},
  VOLUME = {39},
  NUMBER = {2},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_OTHER = {},
  URL = {http://dx.doi.org/10.1029/2003RS002936},
  ABSTRACT = {A method for mapping of ionospheric conditions over Europe,
                  suitable to be used in real time for operational
                  applications, is described in this paper. The method is
                  based on the Simplified Ionospheric Regional Model ( SIRM),
                  a regional model of the standard vertical incidence monthly
                  median ionospheric characteristics that has been updated
                  with real-time ( automatic scaled) ionospheric observations
                  to produce nowcasting maps over Europe. As substantial
                  fluctuations from a monthly median regional ionospheric
                  description occur on day-to-day basis, the SIRM results
                  oversimplified a number of the ionospheric phenomena of real
                  significance for radio communications
                  applications. Therefore a rapid conversion of real-time data
                  from four European digisondes ( Digital Portable Sounders)
                  to the driving parameters of the Simplified Ionospheric
                  Regional Model is introduced as the real-time SIRM updating
                  (SIRMUP). In this approach, values of the ionospheric
                  characteristics from first-guess model parameters at
                  measurement points are combined with real-time
                  measurements. To assess the qualitative improvements
                  achieved with the real-time SIRM update method, observations
                  of foF2 parameter with SIRMUP predictions were compared for
                  various ionospheric conditions. The simulation shows that
                  the SIRMUP prediction results are much improved comparing to
                  SIRM predictions, especially during large-scale ionospheric
                  disturbances, as well as during quiet conditions, while
                  there was a marginal improvement during localized
                  ionospheric disturbances. In general, the results clearly
                  demonstrate that the proposed procedure of updating SIRM
                  with automatic scaling ionospheric parameters from the four
                  European digisondes has the potential to be used in real
                  time for nowcasting the standard ionospheric characteristics
                  over Europe for operational applications.}
}

@ARTICLE{zou00:_annual_f2,
  AUTHOR = {Zou, L. and Rishbeth, H. and Muller-Wodarg, I.C.F. and
                  Aylward, A.D. and Millward, G.H. and Fuller-Rowell, T.J. and
                  Idenden, D.W. and Moffett, R.J.},
  TITLE = {Annual and semiannual variations in the ionospheric
                  F2-layer. I. Modelling},
  JOURNAL = {Annales Geophysicae},
  PAGES = {927--944},
  YEAR = {2000},
  VOLUME = {18},
  NUMBER = {8},
  ABSTRACT = {Annual, seasonal and semiannual variations of F2-layer
                  electron density (NmF2) and height (hmF2) have been compared
                  with the coupled thermosphere-ionosphere-plasmasphere
                  computational model (CTIP), for geomagnetically quiet
                  conditions. Compared with results from ionosonde data from
                  midlatitudes, CTIP reproduces quite well many observed
                  features of NmF2, such as the dominant winter maxima at high
                  midlatitudes in longitude sectors near the magnetic poles,
                  the equinox maxima in sectors remote from the magnetic poles
                  and at lower latitudes generally, and the form of the
                  month-to-month variations at latitudes between about
                  60N and 50S. CTIP also reproduces the
                  seasonal behaviour of NmF2 at midnight and the summer-winter
                  changes of hmF2. Some features of the F2-layer, not
                  reproduced by the present version of CTIP, are attributed to
                  processes not included in the modelling. Examples are the
                  increased prevalence of the winter maxima of noon NmF2 at
                  higher solar activity, which may be a consequence of the
                  increase of F2-layer loss rate in summer by vibrationally
                  excited molecular nitrogen, and the semiannual variation in
                  hmF2, which may be due to tidal effects. An unexpected
                  feature of the computed distributions of NmF2 is an
                  east-west hemisphere},
  UKSSDC_D = {},
  UKSSDC_I = {},
  UK_FIRST = {}
}


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