Dependence of the Geomagnetic Activity on the Structure of Magnetic Clouds

The paper studies high-latitude geomagnetic activity with respect to the structural elements of “fast” solar wind magnetic clouds accompanied by shockwaves. A condition for the occurrence of such clouds and a possible cause of their acceleration in the solar wind have been found. An assumption is made that the turbulent cloud sheaths, the parameters of which are conditioned by the solar wind modified under the influence of the cloud shockwave, contribute to the geomagnetic activity. To estimate the evolution of the accumulating solar wind, the local orientations of the shockwave planes have been determined and the sequence of values of the geoeffective Bz component expected at the magnetospheric boundary in the solar magnetospheric coordinate system has been calculated. Comparison of the AL index dynamics with the values of the Bz component measured by the spacecraft and with the calculated sequence of the Bz values shows that the evolution of the solar wind interplanetary magnetic field (IMF) at the magnetic cloud shockwave over the time of its transport to the magnetosphere must be taken into account.