Abstract:
The K-index is often used as a quantitative measure of local magnetic activity. It is a 3-hour quasi-logarithmic scale developed to measure magnetic activity ranging from 0 to 9, with 0 indicating completely quiet conditions and 9, representing extreme magnetic activity. It is intended to measure geomagnetic disturbances outside the normal diurnal quiet time variations. In order to have a somewhat consistent scale of magnetic activity between observatories at high latitudes, where field variations can be quite large in amplitude, and those at low latitudes, each observatory is assigned its own set of amplitude ranges corresponding to the various K-index levels. Thus, for example, a K-index of 5 at College (TCO) observatory (212.4°E, 64.87°N) corresponds to a lower limit of magnetic activity range of 350 nT over the 3-hour interval, while at San Juan (SJG) observatory (293.85°E, 18.117°N) this same K-index level corresponds to a lower limit of magnetic activity of 40 nT. The idea is to have K-index compensation for the influence of latitude on magnetic activity, so that a K-index of 7 at College and San Juan would represent the same magnetic storm intensity despite the actual differences in the range of magnetic fluctuation amplitudes at the two latitudes.
The eight three-hourly K numbers (after Bartels) are calculated by a computer code (FMI method, Sucksdorff et al., 1991) from the digital recordings of three component flux-gate variometer FGE.
The present tables contain K-indices which are calculated from the data records of PAG observatory (24.177°EN, 42.515°N) since 2007. The real time values of the current K-indices can be seen at http://data.niggg.bas.bg/magn_data1/dailymag_bg.php