A Global Simulation of the Magnetosphere with a Long Tail : Southward and Northward IMF

"Through a global three dimensional MHD simulation, the effect of the Interplanetary Magnetic Field (IMF), both northward and southward, on Earth\u27s magnetosphere has been investigated. A southward IMF, upon reconnect-ing at the dayside magnetopause of the Earth\u27s magnetic field is swept back by solar wind flow and drapes the magnetotail. This gives rise to a plasma sheet cross-tail current increase and explosive magnetic reconnection at around 15R_E. This reconnection results in the formation of a large plasmoid which grows much faster than for the simulation with no IMF, thus supporting, in a convincing way with a minimum of assumptions, previous notions that a south-ward IMF is a driving mechanism of plasma sheet reconnection. A northward IMF is observed to reconnect with the magnetosphere along the cusp shoulder, stripping magnetic field lines away and weakening compression of the plasma sheet. In order to accomodate a balance of magnetic to dynamic pressure along the magnetopause, the magnetosphere changes from its usual comet-like shape to that resembling a tadpole as it attempts to return to a dipolar structure. Plasmasheet reconnection is inhibited.