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About Kp index

The three-hour Kp index was developed in 1949 by Julius Bartelsand is described in his publication 'The standardized index, Ks, and the planetary index, Kp. IATME Bull., 12b, 97– 120'. The publication Matzka et al. (2021) describes the production of the Kp index as well as its history and properties. I particular, the production of nowcast values is described there in detail.

Kp is provided both in near real-time as nowcast values and monthly as definitive values. The derived indices are the ap (linear index), the Ap (daily mean of ap), Cp and C9. A further product derived from Kp are the international quiet and disturbed days. Kp and the derived indices and Products go backt o 1932.

Information on the file format can be found on

Further information pertaining the Kp index can be found here.

Kp is calculated from the K values or the geomagnetic recordings of the following 13 geomagnetic observatories:

geomagnetic Observatory


operating institute



EyrewellEYRGNS ScienceNew Zealand1978
CanberraCNBGeoscience AustraliaAustralia1981
UppsalaUPSGeological Survey of SwedenSweden2004
BrorfeldeBFETechnical University of DenmarkDenmark1984
WingstWNGDeutsches GeoForschungsZentrumGermany1938
NiemegkNGKDeutsches GeoForschungsZentrumGermany1988
LerwickLERBritish Geological SurveyUnited Kingdom1932
EskdalemuirESKBritish Geological SurveyUnited Kingdom1932
HartlandHADBritish Geological SurveyUnited Kingdom1957
OttawaOTTNatural Resources CanadaCanada1969
MeanoookMEANatural Resources CanadaCanada1932
FredricksbergFRDUnited States Geological SurveyUnited States1957
SitkaSITUnited States Geological SurveyUnited States1932

We thank the operating institutes for contributing their indices and data.