March 2021

DOI and new scientific paper for Kp-Index

Kp was assigned a DOI and a dataset publication (Matzka, J., Bronkalla, O., Tornow, K., Elger, K. and Stolle, C., 2021. Geomagnetic Kp index, V. 1.0. GFZ Data Services, ).
A new scientific publications (Matzka, J., Stolle, C., Yamazaki, Y., Bronkalla, O. and Morschhauser, A., 2021. The geomagnetic Kp index and derived indices of geomagnetic activity, Space Weather, ) describes the Kp index and serves as reference for the DOI.

Since January 2020

Warning about ambiguous file names in 2020

Since January 2020, the conventional filenames for the Kp index in the WDC format would have become ambiguous on our server as Kp2001.wdc could mean a monthly file for January 2020 or a yearly file for the year 2001. Therefore are all yearly files on the FTP server available from the subdirectory 'yearly'.

Please find the correspondingly updated format description here:

Despite the fact that each line in these files has its own, correct time stamp, we noticed that some of our users, depending on how they reformat the downloaded data files, have produced corrupted files on their side as a consequence of the filename ambiguity and our mitigation steps. We recommend our users to check their reformatted files, especially for the early 2000s and the early months of 2020 and especially if they are not sure how their downloading and reformatting algorithm deals with the filename ambiguity.


File formats

For information on file formats, see

Publications with descriptions of the K and Kp indices

Bartels, J., 1938. Potsdamer erdmagnetische Kennziffern, 1. Mitteilung. Zeitschr. f. Geophys. 14, 68-78,

Bartels, J., 1939. Potsdamer erdmagnetische Kennziffern, 4. Mitteilung. Zeitschr. f. Geophys. 15, 214-221,

Bartels, J. and Johnston, H.F., 1939. Main features of daily magnetic variations at Sitka, Cheltenham, Tucson, San Juan, Honolulu, Huancayo, and Wateroo. Terr. Mag. 44, p 455 - 469,

Bartels, J., Heck, N.H. and Johnston, H.F., 1939. The three-hour-range index measuring geomagnetic activity. Terr. Magn. Atmos. Electr., 44 (4), p. 411-454,

Bartels, J, Heck, N.H. and Johnston, H.F., 1940. Geomangetic three-hour range indices for the years 1938 and 1939. Terr. Magn. Atmos. Electr., 45 (3), 309-337,

Bartels, J., 1949, The standardized index, Ks, and the planetary index, Kp, IATME Bull., 12b, 97-120.

Bartels, J., 1957a. The technique of scaling indices K and Q of geomagnetic activity, Ann. Intern. Geophys. Year 4, 215-226

Bartels, J., 1957b. 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,

Matzka, J., Bronkalla, O., Tornow, K., Elger, K. and Stolle, C. (2020): Geomagnetic Kp index. V. 1.0. GFZ Data Services.

Matzka, J., Stolle, C., Yamazaki, Y., Bronkalla, O., & Morschhauser, A., 2021. The geomagnetic Kp index and derived indices of geomagnetic activity. Space Weather, 19, e2020SW002641,

Mayaud, P.N., 1980. Derivation, Meaning, and Use of Geomagnetic Indices. Geophysical Monograph Serie, Volume 22, American Geophysical Union, ISBN:9780875900223,

Rangarajan, G.K., 1987. Indices of geomagnetic activity. In: Jacobs, J.A. (Ed.), Geomagnetism, 3, Academic Press, ISBN 0-12-378673-8, 323-384

Siebert M. and Meyer, J., 1996. Geomagnetic Activity Indices. In: Dieminger, W., Hartmann, W. and Leitinger, G.K. (Eds.), The Upper Atmosphere, Springer, Berlin Heidelberg, ISBN 978-3-642-78717-1, 887-911