K-variation includes geomagnetic pulsations, bays or substorms, sudden commencements, geomagnetic storms (with the exception of the recovery phase, see below) and other geomagnetic disturbance from fast changes in the ring-current and other magnetospheric and ionospheric currents. The sum of the K-variation and its counterpart, the non- K-variation, equals the measured geomagnetic field variation at a geomagnetic observatory. Geomagnetic activity is the occurrence of K-variations.” We regard geomagnetic disturbance that is instantaneously driven by the solar wind as K-variation. All other regular and irregular disturbances are non- K-variations. Siebert ( 1971) and Siebert and Meyer ( 1996) use this definition: “ K-variations are all irregular disturbances of the geomagnetic field caused by solar particle radiation within the 3 h interval concerned.
The concept of K-variation, also referred to as geomagnetic activity or disturbance, predates the discovery of the solar wind and historically, K-variation was seen as the effect of 'solar particle radiation' (e.g. Geomagnetic disturbance is also denoted as K-variation. The K index, for which Bartels et al. ( 1939) is an early and excellent description in English, is defined as a quasi-logarithmic measure, ranging in steps of 1 from 0 to 9, of the range of geomagnetic disturbance at a geomagnetic observatory in a three-hourly UT interval (00–03, 03–06, …, 21–24). The methodology to determine Ks and Kp indices is based on earlier indices, namely the global Km index (Bartels et al., 1939) and the reduced Kr and global Kw indices (Bartels et al., 1940). The purpose of the Kp index, or Kp for short, is to monitor subauroral geomagnetic disturbance on a global scale.īartels ( 1949) introduced the standardized Ks and the planetary Kp indices (see also Bartels, 1957a, 1957b Siebert & Meyer, 1996), which are derived from observatory-specific three-hourly K indices (Bartels, 1938, 1939 Bartels et al., 1939, 1940).
Geomagnetic variation consists of quiet variation, which is regular in appearance and mostly of solar electromagnetic radiation origin, and geomagnetic disturbance, which is irregular in appearance and mostly driven by the solar wind.
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