Copyright WDC for STP at RAL.
The Kp index is derived from observatory K indices for a given observatory network. For a given observatory, over each 3-hour period the larger range of irregular variation in the H and D components is ranked into a range class. These range classes are specific to that observatory and rank the variation on a scale from 0 (very quiet) to 9 (very disturbed).
The K index from each observatory is then mapped to a common scale that is intended to eliminate diurnial, seasonal and observatory differences. This scale runs from 0 to 27, sometimes represented as 0,0+,1-,1,...,8+,9-,9, and the values are known as Ks. Finally these Ks values are averaged over the network of observatories to give Kp.
Kp is also sometimes represented on a scale of 0 to 90 where the first digit is 0 to 9 as above and the second digit is 0, 3 or 7. 3 is a one third step up from the first digit, 7 a two thirds step up and 0 is on the first digit. So 23 would be equivalent to 2+ and 27 equivalent to 3-.
The index is unitless and is quasi-logarithmic. For an equivalent index on a linear scale use the Ap index.
The Adolf-Schmidt-Observatory Niemegk of the GeoForschungsZentrum Potsdam took over the responsibility for the calculation and distribution of the Kp and derived activity indices from January 1997
|Kp - equivalent values in different notations|