Origins and Closure of the Region 1 Currents of Iijima and Potemra

Abstract:

Previous studies based on observed statistical properties indicate that the bulk of Iijima and Potemra's region 1 (R1) system of currents is generated by diversion of diamagnetic current in the magnetosphere. Inertial currents flowing in the low-latitude boundary layer have been estimated to contribute at most 20% to the dayside R1 currents, but they do play a special role in diverting field-aligned currents across the magnetopause and through magnetosheath to close in the primary solar wind dynamo acting at the bow of the magnetosphere. Observations and models have been less definitive in interpreting the sources of overlapping upward and downward “sheets” of R1 current flowing into Harang reversal region in the midnight sector. This highly dynamic region continues to challenge our understanding of plasmasheet current generators which typically violate the assumption made in the aforementioned observational studies that the plasma state is in near equilibrium.

Long duration, global MHD simulations driven by actual, variable interplanetary conditions are shown to give average field-aligned current distributions at the ionosphere that closely resemble Iijima and Potemra’s patterns, especially when simulation grids with relatively high resolution are used. This similarity suggests that simulation results can be compared with observationally inferred sources of R1 currents to evaluate the conditions under which equilibration is approximately valid or when the current generators are strongly time-varying and deviate from statistical averages. The differences are shown to be especially significant in the nightside plasmasheet at distances of 10 Re or more from Earth where axial/meridional current systems are closely connected with spatially varying inertial currents.