Impact of Interplanetary Magnetic Field By on Subauroral Polarization Streams at Dawn and Dusk

Abstract

This study uses 8 years of DMSP data to examine how the polarity of the interplanetary magnetic field (IMF) B_y influences the strength and latitude of subauroral polarization streams (SAPS), alongside field-aligned currents (FACs). Significant local time, seasonal, and hemispheric differences are observed. At dusk, R1 (Region 1) FACs are found poleward and R2 (Region 2) FACs equatorward of peak SAPS; at dawn, SAPS are positioned equatorward of upward R2 FACs. In the Northern Hemisphere (NH), SAPS are stronger under IMF B_y > 0 at dusk, while in the Southern Hemisphere (SH), SAPS are stronger under IMF B_y < 0. Dawnside SAPS tends to be stronger under IMF B_y < 0. Duskside R1 FACs are stronger under IMF B_y < 0, with seasonal variations in R2 FACs, whereas dawnside R2 FACs prefer IMF B_y > 0. SAPS latitudes vary seasonally with IMF B_y polarity, showing more poleward SH SAPS under IMF B_y > 0. Ionospheric upflows exhibit similar IMF B_y polarity dependence as SAPS at dusk, but this influence diminishes at dawn. Model simulations underscore how IMF B_y affects SAPS dynamics through FACs and conductivity gradients, highlighting larger NH (SH) SAPS under positive IMF B_y at dusk (dawn) compared to its SH (NH) counterpart.