Abstract
We study the development of strong geomagnetic storms due to coronal mass ejections in near-Earth space. We compare the time evolution of geomagnetic disturbances with the time variation of solar wind plasma and field parameters with special attention to the development of the main-phase of the geomagnetic storms. We use geomagnetic indices and solar wind parameters of three different time resolutions (1 hour, 5-minutes, and 1-minute) for the analysis, and determine the time-lag between them during the development of the geomagnetic storms. The time-lag has been determined for the 10 selected geomagnetic storms of different strength (weakest geomagnetic storm with
Dst
=
−
88
nT and strongest geomagnetic storm with
Dst
=
−
422
nT) and different main-phase durations (shortest main-phase duration ≈ 4 hours, and longest main-phase ≈ 21 hours). These results will lead us towards better understanding of onset and the development of geomagnetic storms and ultimately the solar wind-magnetosphere coupling.