Magnetospheric convection in the presence of interplanetary magnetic field B-y: A conceptual model and simulations

Existing observations from ISEE 3 and new observations from Galileo show that when the interplanetary magnetic field (IMF) has a B-y component, a B-y component also develops in the Earth's magnetotail, but only in those quadrants in which the addition of the newly opened magnetic flux tubes occurs. The presence of B-y on the closed field lines (which is in the same direction as the IMF B-y) is also seen. We suggest that for a positive IMF B-y, the magnetopause is open only in the north dawn and south dusk quadrants of the magnetotail. The continuity of magnetic field across the open boundary then requires that a B-y component be present in the magnetosphere in these quadrants but not in the other two quadrants. We present a model of the magnetospheric convection that postulates cross-tail flows in the mantle/lobe system and the plasma sheet. We suggest that shear flows between the northern and the southern halves of the plasma sheet generate a B-y component on the closed magnetic field lines. The model is consistent with the two-cell ionospheric convection models constructed from electric field observations by Heppner and Maynard [1987]. Results from global MHD simulations confirm the main features of the proposed model.