A GLOBAL MAGNETOHYDRODYNAMIC SIMULATION OF THE RESPONSE OF THE MAGNETOSPHERE TO A NORTHWARD TURNING OF THE INTERPLANETARY MAGNETIC-FIELD

We have used a global magnetohydrodynamic simulation model to investigate the time series of events which occur in the magnetosphere when the interplanetary magnetic field (IMF) changes from southward to northward. Within 15 min of the northward turning the magnetopause reconnection site moves from the subsolar point to the high-latitude tail. The high-latitude reconnection converts tail lobe field lines into closed dayside field lines and new field lines in the IMF. The removal of lobe flux plus continuing reconnection at the near-Earth neutral line cause the field lines which thread the plasma sheet to relax to a more dipolar state and a very slow tailward retreat of the near earth neutral line. The newly closed dayside field lines are convected around the flanks of the magnetosphere and into the tail. The closed flux convected from the dayside to the tail is the main source of closed flux into the tail. As a result, the plasma sheet recovers first along the flanks of the magnetosphere and then nearer midnight. The near-Earth neutral line shrinks toward midnight and then moves rapidly tailward.