The Magnetospheric Response to Abrupt Variations in the IMF Orientation

Abstract:

We run the University of Michigan's BATS-R-US global magnetohydrodynamic model at NASA/GSFC's CCMC
to study the magnetospheric response to abrupt variations in the IMF orientation but constant solar wind plasma
parameters. IMF rotations from southward to duskward orientations diminish reconnection rates and the flow of
plasma to the dayside magnetopause, launch Alfven waves that carry strong duskward magnetic field perturbations
to the cusp ionosphere, introduce a weak duskward magnetic field perturbation to the outer dayside magnetosphere, twist
the magnetotail current sheet counterclockwise when viewed from the Sun, flatten the north/south dimensions of the distant magnetotail, and
generate a broad slow-mode fan on the magnetotail flanks. Southward IMF turnings strengthen the Region 1 Birkeland
currents, prominently depressing magnetic field strengths in the inner dayside magnetosphere and to a lesser
degree those in the outer magnetosphere, consistent with inward dayside magnetopause erosion. The dayside
magnetopause becomes blunter. As evidenced by enhanced magnetosheath thermal and magnetospheric
magnetic pressures, the magnetopause therefore becomes subject to a greater fraction of the incident solar wind
dynamic pressure at locations away from the subsolar point.