Abstract

Experimental results indicative of two mechanisms of the solar wind impact on magnetosphere

Author(s): Troshichev Oleg A

The paper presents a short review of experimental data indicative of two independent mechanisms ensuring the solar wind influence on the magnetosphere, such as the reconnection of interplanetary (IMF) and terrestrial magnetic fields (Dungey,1961) and formation of the plasma pressure gradients in the magnetosphere as a generator of magnetospheric electric fields and currents (Tverskoy, 1972). According to spacecraft measurements, different Field-Aligned Current (FAC) systems act independently in the magnetosphere. The main is the R1 FAC system, operating within the magnetosphere irrespective of season and IMF orientation, the polar cap magnetic disturbances of DP0/DP2 type being permanently generated by this FAC system. The NBZ and BY FAC systems, observed at conditions of the northern (BZN) and azimuthal (BY) IMF influence, generate DP3 and DP4 magnetic disturbances, but only in the sunlit summer polar cap with the high-conductive ionosphere. The existence of the R1 FAC system, related to the plasma sheet within the magnetosphere, is logically treated in the framework of the Tverskoy concept, whereas the occurrence of the NBZ and BY FAC systems, related to the boundary layers of the magnetosphere, is explained in the framework of Dungey concept. To characterize the total solar wind energy input into the magnetosphere, the polar cap magnetic activity PC index, evaluated by the DP2 disturbances power, has been introduced. The PCN and PCS indices, derived online by data on DP2 disturbances in the Northern and Southern polar caps, are usually consistent, follow changes in the solar wind impact on the magnetosphere and well correlate with the development of magnetic storms and substorms. This makes it possible to regard the PC index as a proxy of the solar wind energy input into the magnetosphere. However, strong DP3 and DP4 disturbances in the summer polar cap, related to the mechanism of Dungey, occasionally distort the regular structure of DP2 disturbances, related to the mechanism of Tverskoy. It implies that the PC index derived in the winter polar cap (PCwinter) should be used to monitor the actual state of the magnetosphere.