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 Kp INDICE

Kp Indices are calculated by www.gfz-potsdam.de/pb2/pb23/GeoMag/niemegk/kp_index

The planetary three-hour-range index Kp is the mean standardized K-index from 13 observatories between 44° and 60° northern or southern geomagnetic latitude The scale is 0o to 9o, expressed in thirds of a unit, e.g. 5- is 4 2/3, 5o is 5, 5+ is 5 1/3. This planetary index has been designed to measure solar particle radiation by its magnetic effects. The other indices derived from Kp are the three-hour index ap (the equivalent range), the daily indices Ap, the Cp and C9 characters that are related to the daily sum of ap.

The three-hour equivalent amplitude ap is deduced from Kp as follows :

 Kp 0o 0+ 1- 1o 1+ 2- 2o 2+ 3- 3o 3+ 4- 4o 4+ ap 0 2 3 4 5 6 7 9 12 15 18 22 27 32 Kp 5- 5o 5+ 6- 6o 6+ 7- 7o 7+ 8- 8o 8+ 9- 9o ap 39 48 56 67 80 94 111 132 154 179 207 236 300 400

In order to use ap as an equivalent amplitude, it is considered in relation to the conditions at a standard station, which is a station having the lower limit of 500 nT for K = 9. At such a station the average range in nT of the most disturbed of the two horizontal components in a three-hour interval can be taken as 2 ap (for instance, for Kp = 3+, ap=18, ie 36 nT). In other words ap is an equivalent amplitude in the unit 2 nT. The column headed Ap gives the daily average for the eight values ap per day. Therefore, Ap may be called the "equivalent daily amplitude Ap", expressed in the unit 2 nT for a standard station. It is recommended to use Ap in preference to the sum of the indices Kp. The last column gives the daily planetary character figure Cp, as defined in Bulletin 12e, page 111. It should be noted that Cp, introduced for a standardization of the international character figures Ci, has not been approved by the Association. Instead, Ap was preferred. For a rough conversion of Ci figures (prior to 1932) into Ap, the following table (derived from Bulletin 12e, page 111, their Table 2) may be used :

 10.Ci 0 1 2 3 4 5 6 7 8 9 10 Ap 2 4 5 6 8 9 11 12 14 16 19 10.Ci 11 12 13 14 15 16 17 18 19 20 Ap 22 26 31 37 44 52 63 80 110 160

Monthly tables of Kp and derived indices are given in Monthly tables of Kp and derived indices . Kp values are displayed as "musical diagrams" according to Bartels solar rotation on request at GeoForschungZentrum, Potsdam GFZ (Kp, Ap; Potsdam, Germany)

Note - Observatories wishing to compute local equivalent amplitudes ak from their local K indices, may use the conversion table given below, which consists in the amplitudes (in nT) of the middle of each K class, as firstly proposed by Bartels (IATME Bull. 12e, 1951), and following a IAGA WG 5.5 recommandation (Buenos Aires, 1993).

 K 0 1 2 3 4 5 6 7 8 9 ak 2.5 7.5 15 30 55 95 160 265 415 666

These values are given here for a K = 9 lower limit L9 = 500 nT; at stations having a different value of L9, they should be multiplied by L9/500, in order to have ak in nT .

List of Kp observatories

 Northern Hemisphere Southern Hemisphere Observatory Corr. Geom. Lat. Observatory Corr. Geom. Lat. MEA Meanook 62.5° EYR Eyrewell 50.2° SIT Sitka 60.0° CAN Canberra 45.2° LER Lerwick 58.9° OTT Ottawa 58.9° LOV Lovö 56.5° ESK Eskdalemuir 54.3° BJE Brorfelde 52.7° FRD Fredericksburg 51.8° WNG Wingst 50.9° HAD Hartland 50.0° NGK Niemegk(4) 48.8°

(4) Niemegk has replaced Witteveen in the Kp network since April 1st, 1988.

Distribution of Kp observatories