Historical K index data collection of Soviet magnetic observatories, 1957-1992

The presented collection includes the results of the K index determination at 41 geomagnetic observatories of the former USSR for the period from July 1957 to early 1990s. This unique collection was formed at the World Data Center for Solar-Terrestrial Physics in Moscow. The historical data, which are offered to the international scientific community, cover the second half of the 20th century and can be used for retrospective analysis and study of geomagnetic events in the past as well as for data validation or forecasting.