Impact of Interplanetary Magnetic Field B_y 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) By 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 By > 0 at dusk, while in the Southern Hemisphere (SH), SAPS are stronger under IMF By < 0. Dawnside SAPS tends to be stronger under IMF By < 0. Duskside R1 FACs are stronger under IMF By < 0, with seasonal variations in R2 FACs, whereas dawnside R2 FACs prefer IMF By > 0. SAPS latitudes vary seasonally with IMF By polarity, showing more poleward SH SAPS under IMF By > 0. Ionospheric upflows exhibit similar IMF By polarity dependence as SAPS at dusk, but this influence diminishes at dawn. Model simulations underscore how IMF By affects SAPS dynamics through FACs and conductivity gradients, highlighting larger NH (SH) SAPS under positive IMF By at dusk (dawn) compared to its SH (NH) counterpart.