Fast Solar Wind and Geomagnetic Variability during the Descendant Phase of the 11-yr Solar Cycle

摘要

Solar activity and its consequences for the interplanetary space are governing and perturbing the Earth's magnetosphere. The response of the terrestrial magnetosphere displayed as geomagnetic disturbances is measured by several geomagnetic indices. This paper analyses the geomagnetic variability during the descendant phases of the last four solar cycles (Nos. 20-23) under the influence of the high speed streams of the solar wind. The descendant phases of the 11-yr solar cycle are complex intervals of the irrespective cycles during which two magnetic dipoles with opposite polarities are present on the Sun. The variability and statistics of the stream intensity and geomagnetic index Ap during the descendant phases revealed strong activity. The correlation between the geomagnetic indices and the stream intensity during the analyzed intervals was examined. The energy transfer from solar wind into the terrestrial magnetosphere during the main phase of some geomagnetic storm depends of the solar wind energy and magnetic fields (terrestrial and heliospheric) configuration which allows or not reconnections of these fields. Analysis of some geomagnetic storms during the descendant branch of solar cycle 23 put into evidence the main role of the B_z component of heliospheric magnetic field in this transfer.