UK Solar System Data Centre
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 | |||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 |
| 0 | 0+ | 1- | 1 | 1+ | 2- | 2 | 2+ | 3- | 3 | 3+ | 4- | 4 | 4+ | 5- | 5 | 5+ | 6- | 6 | 6+ | 7- | 7 | 7+ | 8- | 8 | 8+ | 9- | 9 |
| 0 | 3 | 7 | 10 | 13 | 17 | 20 | 23 | 27 | 30 | 33 | 37 | 40 | 43 | 47 | 50 | 53 | 57 | 60 | 63 | 67 | 70 | 73 | 77 | 80 | 83 | 87 | 90 |