Magnetospheric convection during prolonged intervals with southward interplanetary magnetic field

摘要

We have used a global magnetohydrodynamic simulation to investigate magnetospheric convection during a prolonged interval with modest southward driving. The interval simulated occurred on 13 and 14 February 2001 during a period when the interplanetary magnetic field (IMF) remained weakly southward for over 12 hours. Early in the simulation a near-Earth neutral line located between 20 R E and 40 R E in the tail drove flows earthward and then around the near-Earth obstacle to return magnetic flux to the dayside. The earthward flow led to increased ionospheric conductance and developed a modest earthward pressure gradient in the inner plasma sheet. Ionospheric line tying slowed the earthward flow. The pressure gradient caused the inner tail to become interchange unstable and lead to the tailward flow. When the tailward moving flux tube reached the near-Earth neutral line additional reconnection occurred between the tailward moving flux tube and IMF field lines created by lobe reconnection thereby returning flux to the nightside tail lobes. Late in the event the new lobe field lines reconnected at the duskside magnetopause creating additional rapid tailward motion. The tailward flow led to a reduction in both the ionospheric conductance and near-Earth tail pressure gradient and earthward flow was again established. This sequence repeated at least three times during the interval simulated.