@COMMENT{{{This file has been generated by bib2bib 1.74}}
@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 25±2% 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 16±2%. 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°%Gâ%@55%Gâ%@°N),
induced by geomagnetic activity, by using the relative
deviations (µ) 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 µ and Kp is obtained by using 11
years of data from 26 midlatitude ionosondes. The
statistical analysis reveals that the average dependence of
µ 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 µ along local times can be assumed
sinusoidal. A continuity equation is written for µ with
the Èproduction termÉ being a function of Kp modulated
by a sinusoidal function of local time and the ÈlossÉ
term proportional to µ with a loss coefficient
Â=1/T. A new, modified function of geomagnetic activity
(Kf) is introduced, being proportional to µ averaged over
all longitudes. The model µ 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 Èprediction efficiencyÉ
(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%Gâ%@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 %GÆ%@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
60°N and 50°S. 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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