AURORAL DYNAMICS AT DIFFERENT STAGES OF STORM RECOVERY PHASE VERSUS THE STRENGTH OF THE MAIN PHASE

Introduction Magnetic storms are induced by interaction of interplanetary solar plasma flows with the Earth’s magnetosphere. The strength of magnetic storm is determined by ring current development, which in turn, is characterized by the Dst-index. Storm recovery phase is traditionally considered to be connected with the ring current decay, which can be physically due to a combination of several different energetic particle loss processes (Coulomb collisions, charge exchange and wave-particle interactions). Usually two stages of storm recovery phases are observed: the early (fast) recovery phase and the late (slow) one. As known, the ring current consists of two different atomic ion components having different characteristic decay time that probably can be a reason for two-step storm recovery phase (Hamilton et al., 1988; Daglis, 1997). Contrary to this commonly accepted interpretation Feldstein and Dremukhina, (2000) suppose that the two-phase decay of the Dst variations during the magnetic storm recovery phase is controlled by the decay of a two current system: the ring current (DR) and the magnetospheric tail current (DT). Two types of magnetic storms, depending on their origins, take place: CME-driven storms and CIR-driven storms. Major/intense geomagnetic storms are mainly caused by coronal mass ejections (CME), while moderate and minor storms can be induced by both coronal mass ejections (CME) and corotating interaction region (CIR) associated with recurrent high-speed streams. CME and CIR events in the solar wind, the magnetosphere and the auroral zone are reviewed in (Borovsky J.E., and Denton M.H., 2006). Spectral characteristics of aurora and their connection with solar wind streams were investigated in (Hviyuzova, and Leontiev, 1997; 2001). Relationship between auroral bulge parameters and high-speed solar wind streams was studied in (Despirak et al., 2007). Here we present a comparative analysis of spatio-temporal auroral dynamics in the dusk-midnight MLT sector during the early and late recovery phases of 10 magnetic storms of different intensity and driven by both CME and CIR geomagnetic events, considering Dst minimum value to be the energy characteristics of the storm main phase