spase://GBO/NumericalData/Indices/Kp.Ap

Kp, Sum_Kp, (3-hour) ap, and (Daily) Ap geomagnetic indices. Kp and ap are 3-hour planetary indices and Sum_Kp and Ap are daily summed and averaged (respectively) indices created from Kp. These indices were created at the Geophysical Institute of Gottingen University through 1996, and at GeoForschungsZentrum (GFZ, Potsdam) subsequently. GFZ, url given below, is the primary distribution site. The web site of WDC for Geomagnetism at Kyoto U., url given below, offers plots and numeric downloads for Kp and related indices. The data are currently (as of 12/07/2011) "final" from January, 1957, through December, 2008, and are "real time" thereafter, through the current day. Alternative sources of many of the Kp and related indices include the hourly OMNI data set at NASA/GSFC/SPDF. Worldwide Indices The subscript p means planetary and designates a global magnetic activity index. The following 13 observatories, which lie between 46 and 63 degrees north and south geomagnetic latitude, now contribute to the planetary indices: Lerwick (UK), Eskdalemuir (UK), Hartland (UK), Ottawa (Canada), Fredericksburg (USA), Meanook (Canada), Sitka (USA), Eyrewell (New Zealand), Canberra (Australia), Lovo (Sweden), Brorfelde (Denmark), Wingst and Niemegk (Germany). Three-hour-range Index Kp Kp index derives from Ks indices that isolate solar particle effects on the earth's magnetic field; over a 3-hour period, they classify into disturbance levels the range of variation of the more unsettled horizontal field component. Each activity level relates almost logarithmically to its corresponding disturbance amplitude. Three-hour indices discriminate conservatively between true magnetic field perturbations and the quiet-day variations produced by ionospheric currents. Ks indices range in 28 steps from 0 (quiet) to 9 (greatly disturbed) with fractional parts expressed in thirds of a unit. A Ks-value equal to 27, for example, means 2 and 2/3 or 3-; a Ks-value equal to 30 means 3 and 0/3 or 3 exactly; and a Ks-value equal to 33 means 3 and 1/3 or 3+. The arithmetic mean of the Ks values scaled at the 13 observatories listed above gives Kp. Equivalent Amplitude ap The ap-index ranges from 0 to 400 and represents a Kp-value converted to a linear scale in nT (nanoTesla) - a scale that measures equivalent disturbance amplitude of a station at which K=9 has a lower limit of 400 nT.