Solar wind-magnetosphere energy coupling under extreme interplanetary conditions: MHD simulations

In this paper, we present results derived from global magnetohydrodynamic s imulations of the response of the magnetosphere to magnetic clouds. The sim ulations were driven with solar wind data from 10 January 1997 and 4 May 19 98. Both periods were major magnetic storms. We find that during moderate p eriods of magnetic merging between the interplanetary magnetic field (IMF) and the magnetospheric magnetic field, the simulated magnetosphere responds with a loading-unloading behavior characteristic of substorms. However, du ring periods of strong, sustained, southward IMF, the simulation evolves to a directly driven state, without the loading-unloading component. This beh avior is the same as that of the real magnetosphere (Bargatze, L.F., Baker, D.N., McPherron, R.L,, Hones, E.W., Jr., 1985. Magnetospheric response for many levels of geomagnetic activity. J. Geophys. Res., 90, 6387-6394), thu s providing compelling evidence that the simulation is accurately represent ing the fundamental features of solar wind-magnetosphere coupling. (C) 2000 Elsevier Science Ltd. All rights reserved.