Configuration instability of the near-earth magnetotail in the presence of an earthward plasma flow and substorm onset

The one-fluid MHD approach is Used to investigate configuration instability in the near-Earth magnetotail in the presence of plasma flows prior to onset of the substorm expansion phase. The results show that drift ballooning modes become absolutely unstable and grow more rapidly in the presence of an earthward plasma flow. On the basis of these results and the configuration instability model of substorm expansion onsets, we suggest that magnetic reconnection in the midtail and resulting plasma flows may lead to rapid development of dipolarizaton of the magnetic field in the near-Earth tail (Pu et at, 1996, 1997), causing intense substorm expansion onsets. This model integrates the NECD and NENL models, giving a physical picture for the initiation of intense substorms. Comparison of the theory with GEOS 2 measurements indicates that a number of substorm observations are consistent with this substorm expansion scenario.