Impact of Interplanetary Magnetic Field <i>B</i>_<i>y</i> 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 &gt; 0 at dusk, while in the Southern Hemisphere (SH), SAPS are stronger under IMF B y &lt; 0. Dawnside SAPS tends to be stronger under IMF B y &lt; 0. Duskside R1 FACs are stronger under IMF B y &lt; 0, with seasonal variations in R2 FACs, whereas dawnside R2 FACs prefer IMF B y &gt; 0. SAPS latitudes vary seasonally with IMF B y polarity, showing more poleward SH SAPS under IMF B y &gt; 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.