The planetary activity index Kp - long-term monitoring of solar influence on the Earth’s magnetic field

Julius Bartels introduced in 1949 the planetary geomagnetic activity index Kp and the derived activity
numbers ap, Ap, Cp and C9. These activity numbers were accepted by the IAGA as official measures to express
the geomagnetic activity. The data series expand back to 1932. Kp and its derived numbers got a world wide
usage in geomagnetic science. The 10 International Quietest and 5 Most Disturbed Days of every month are
determined on the base of this index. The series of definitive indices is routinely updated twice a month on
the web. A quick-look indices calculation runs automatically in order to meet the requests of a near real-time
availability. The K numbers of the 13 Kp observatories are calculated on the basis of their minute values every
3 hours with a time delay of about 15 minutes. The Kp are calculated by means of the regular algorithm from
these K numbers. The Kp, ap, Ap and Cp calculated this way are immediately provided on the web. The
quick-look indices are replaced by the definitive numbers after their usual calculation every half month.