Kp index correlations with solar-wind parameters during the first and second stages of a recurrent geomagnetic storm

Abstract

The dependence of geomagnetic activity during a recurrent magnetic storm on the solar-wind magnetic field and plasma parameters has been studied. According to variations of solar-wind magnetic field strength B, a recurrent magnetic storm is divided into two stages: the first proceeding during the peak of B, and the second proceeding after the return of B to quiet level. The K p index vs solar-wind parameters scattering diagrams for stages I and II differ significantly. In particular, the random scattering for stage I is much larger than for stage II. It was found that for stage I the K p index correlates with B, with the sign and value of northsouth field component B z and with the magnitude ΔB of field fluctuations, the situation being similar to that during sporadic magnetic storms, though the scale of the event is smaller. For stage II, the K p index does not correlate with B, but strongly correlates with ΔB and weaker—with B z . So geomagnetic activity at stage II is supported mainly by solar-wind magnetic field fluctuations. The dependence of the K p index on plasma parameters (concentration of protons n, bulk velocity v and temperature T) is weak for both stages.