Indices of Global Geomagnetic Activity

Geomagnetic Kp Index

The planetary three-hour-range Kp index was introduced by J. Bartels in 1949 and is derived from the standardized K index (Ks) of 13 magnetic observatories. It is designed to measure solar particle radiation by its magnetic effects.

Musical Kp Diagram

The most popular representation of the Kp indices is in form of the Bartels musical diagram (musical scales).

Geomagnetic ap, Ap, Cp and C9 Indices

The geomagnetic ap, Ap, Cp and C9 indices and the classification of international Q-days and D-days are derived from the Kp index.

Related Indices

Km is an index similar to Kp, except for the different number and selection of stations and the method of averaging. The indices am and Am are similar to ap and Ap. Km, am and Am are evaluated at l'Institut de Physique du Globe in Paris, France.


Sources of Kp and derived indices

Structure of the FTP sites

Historical and current Kp are supplied by the International Service of Geomagnetic Indices. Calculation and distribution of the indices are now performed by the GeoForschungsZentrum Potsdam. Two anonymous FTP servers with identical structure are available:
( WWW access: )
Note: FTP sites may refuse connections due to excessive traffic.
;-) Your mileage may vary with a different FTP program.

The kp-ap/ directory contains

readme.txt (text file)
A plain text copy of the Geomagnetic Indices WWW page.
music.exe (binary executable file)
A PC executable program for 386 or higher machines. music.exe reads Kp/ap values in WDC format and produces a PostScript file with Bartels Kp music diagram. Download music.exe using binary mode! The data file ssc.dat is also required to run music.exe.
ssc.dat (text data file)
List of sudden commencements (ssc), partly preliminary.
tab/ (subdirectory)
contains the monthly Kp/ap tables in a simple text format readable for both humans and computers (*.tab). The file tab_fmt.doc provides a format description. The tables distributed by regular mail (PostScript format) are also provided in this directory.
wdc/ (subdirectory)
contains the monthly (respectively yearly) Kp/ap tables and much more information in condensed tables (ASCII format). The format is nearly identical to the format of Kp/ap tables distributed by the World Data Center A for Solar-Terrestrial Physics. The file wdc_fmt.doc provides a format description. This format does not contain any information on the quiet and most disturbed days as the tables in the tab directory do.
music/ (subdirectory)
contains the Kp values in the Bartels musical diagram (PostScript format), which is very helpful in visualizing the indices.
quietdst/ (subdirectory)
contains tables of the quietest and most disturbed days for all months since Jan 1932. (Values since 1900 also supplied, use with caution.)
kp-freq/ (subdirectory)
contains tables of frequencies of Kp indices.
ap_monyr.ave (text file)
A table with monthly and yearly averages of Ap.

Related WWW Servers

For questions concerning specific data or the contents of this page, please contact:
Kevin Ivory,
Last modified: 29 Apr 1997