A GLOBAL MAGNETOHYDRODYNAMIC SIMULATION OF THE MAGNETOSPHERE WHEN THEINTERPLANETARY MAGNETIC-FIELD IS SOUTHWARD - THE ONSET OF MAGNETOTAILRECONNECTION

We have used a new high-resolution global magnetohydrodynamic simulati on model to investigate the onset of reconnection in the magnetotail d uring intervals with southward interplanetary magnetic field (IMF). Af ter the southward IMF reaches the dayside magnetopause reconnection be gins and magnetic flux is convected into the tail lobes. After about 3 5 min, reconnection begins within the plasma sheet near midnight at x = -14R(E). Later the x line moves toward dawn and dusk. The reconnecti on occurs just tailward of the region where the tail attaches onto the dipole-dominated inner magnetosphere. The simulation shows that prior to the onset of reconnection, the Poynting flux is concentrated in th is region. The time required for the start of reconnection depends on the component of the magnetic field normal to the equator (B(z)). Reco nnection occurs only after the B(z) component has been reduced suffici ently for the tearing mode to grow. Later, when all the plasma sheet f ield lines have reconnected, a plasmoid moves down the tail.