Abstract

Relationships between characteristic parameters of geomagnetic storms like the pressure corrected Dst index (Dst*), the solar wind speed, the southward component of the interplanetary magnetic field B-s, and their associated times were studied during two solar cycles and for approximately 300 storm events extracted from the OMNI database (1974-1996) to further analyze what drives Dst* not only during storms but also during non-storm times. Analyzing the whole data set, that is considering storm time and the less disturbed (nonstorm) times, we infer that outside the storm phases the dominant driver role is played by the solar wind speed and that its role during storms is usually not negligible. However, as expected, during the main and recovery phases of magnetic storms the driving parameter is the dawn-dusk component of the interplanetary electric field vB(s), where the main role is played by B-s. We found that the Dst* peak grows monotonically with the peak of B-s. The duration time t(Bs), that B-s remains over a certain threshold value grows linearly with the peak of Dst* for weak, moderate and some intense storms. For more intense events the growth rate diminishes and probably vanishes. Significant differences appear when the correlation between the peaks of Dst* and B-s is analyzed during the different solar cycle phases. That correlation and also the recurrence of our chosen storms have a periodic behavior, similar to the solar cycle. The most of storms are registered during the ascending phases of the solar cycle and sunspot maxima, however the higher correlations between the peaks of B-s and Dst* are found during minima and ascending phases of the solar cycle. (C) 2014 Elsevier Ltd. All rights reserved.