Dynamics of the magnetosphere during geomagnetic storms on January 21-22, 2005 and December 14-15, 2006

The dynamics of large-scale magnetospheric current systems during geomagnetic storms on January 21-22, 2005 and December 14-15, 2006 is investigated using the A2000 model of the magnetospheric magnetic field. Storm development is controlled by both the interplanetary magnetic field and solar wind pressure that create conditions for injection of plasma into the inner magnetosphere. It is demonstrated that the main role in the development of the January 21-22, 2005 magnetic storm was played by a strong impulse of solar wind pressure, while the December 14-15, 2006 storm was initiated by a changed orientation of the interplanetary magnetic field. As a consequence, the Dst variation of the geomagnetic field during the January 21-22, 2005 storm is determined basically by ring current development. On December 14-15, 2006 it is determined by comparable contributions of the ring current and of the magnetotail currents. The results of modeling are confirmed by data on dynamic properties of the fluxes of three populations of ions with energies 30-80 keV (at low latitudes L < 2, and at latitudes below and above the isotropic precipitation boundary) measured by the solar-synchronous satellites of NOAA (POES 15, POES 16, and POES 17).