Service International des Indices Géomagnétiques
International Service of Geomagnetic Indices

Kp index

Kp time resolution: 3-hour (UT) interval
unit: quasi-logarithmic scale as a third of K units (28 values):
0o, 0+, 1-, 1o, 1+, 2-, ... , 8+, 9-, 9o.
Available from 1932 onwards
Type of index K-derived planetary
Purpose To characterize the intensity of geomagnetic activity on a planetary scale (however because of the historical context at the time of its creation, the Kp network is heavily weighted towards Europe and Northern America).
Network Made of 11 northern and 2 southern stations between 44° and 60° northern or southern geomagnetic latitude.
(see list of actual and previous Kp magnetic observatories)
Derivation Kp is the arithmetic mean of the 3-hour standardized K-indices for the 13 Kp-observatories.

The standardization is achieved using standardization tables (*) for each observatory that were defined by Bartels (1949). They aim at removing the UT and seasonal variations in the geomagnetic disturbances.

(*) More specific and detailed information may be found on the GFZ website devoted to Kp and related geomagnetic indices.
ISGI Collaborating Institute GFZ Potsdam, Germany
IAGA endorsed IATME Bulletin 14, 1954, p. 368, resolution 6 and p.229
Related geomagnetic indices
(enclosed in main index downloaded file)
ap time resolution: 3-hour (UT) interval
unit: linear scale in unit ~ 2nT, obtained from Kp through a conversion table (Kp2ap)
Ap time resolution: 1 day (UT) interval
unit: linear scale in unit ~ 2nT, obtained from daily average of eight ap values
Cp time resolution: 1 day (UT) interval
unit: linear scale in steps of one-tenth (from 0 = quiet, to 2.5 = disturbed), obtained from Ap through a conversion table (sum(ap)2Cp)
C9 time resolution: 1 day (UT) interval
unit: linear scale in steps of one (from 0 = quiet, to 9 = disturbed), obtained from Cp through a conversion table (Cp2C9)
Citation Matzka, J., O. Bronkalla, K. Tornow, K. Elger and C. Stolle (2021) - Geomagnetic Kp index. V. 1.0, GFZ Data Services, DOI:10.5880/Kp.0001
Historical references • Bartels, J. (1949) - The standardized index Ks and the planetary index Kp, IATME Bulletin 12b, 97.
• Bartels, J. and J. Veldkamp (1954) - International data on magnetic disturbances, fourth quarter, 1953, J. Geophys. Res., 59, 297-302, DOI:10.1029/JZ059i002p00297.
• Bartels, J. (1957) - The technique of scaling indices K and Q of geomagnetic activity, Ann. Intern. Geophys. Year 4, 215-226. Get PDF (672.2KB)
• Bartels, J. (1957) - The geomagnetic measures for the time-variations of solar corpuscular radiation, described for use in correlation studies in other geophysical fields, Ann. Intern. Geophys. Year 4, 227-236. Get PDF (576.8KB)