Copyright WDC C1 for STP at RAL.
'The IAGA Bulletins No 18 (for the years 1932-1961) {Bartels, 1962}, No 12q1 (for 1962) {Bartels et al, 1965}, No 12r1 (for 1963) {Bartels et al, 1966}, and the official publications prepared by the Institute for Geophysics of the University of Gottingen (for 1964 to the present) have been used for the Kp values and the derived indices.
The sun spot numbers have been taken from the official publications of the Swiss Federal Observatory, Zurich (Waldmeier, 1961).
The solar 10.7cm flux from Ottawa since 1947 has been punched from the publications of the Institute for Telecommunication Sciences and Aeronomy, Boulder, Colorado. As far as indicated, the flux adjusted to one astronomical unit has been used.'
From January 1997 the Adolf-Schmidt-Observatory Niemegk of the GeoForschungsZentrum Potsdam took over the responsibility for the calculation and distribution of the Kp and derived activity indices. The complete Kp series is published in the IAGA Bulletins.