Solar wind driving of dayside field-aligned currents

Variations in the dayside field-aligned current (FAC) density (J//), field-aligned parallel potential drop (Δφ//), peak precipitating electron energy (peak Ee), and precipitating electron energy flux (ɛ) as functions of solar wind (SW) and interplanetary magnetic field (IMF) are investigated with DMSP observations and a quasi-stationary low latitude boundary layer (LLBL) - FAC coupling model. Region-1 (R1) J// responses to variations in SW velocity (Vsw) and density (nsw) at 08 - 16 MLT suggest that R1 at these local times are frequently open while R1 at 06 - 08 and 17 - 18 MLTs are frequently closed. R2 is located mostly on closed field lines. In the afternoon open R1 at 12 - 16 MLTs, an increase in nsw increases J//, decreases maximum peak Ee (proxy for Δφ//), but has little effect on maximum ɛ. In the same R1 region, an increase in Vsw increases J//, maximum peak Ee, and maximum ɛ. The dependencies of J//, maximum peak Ee, and maximum ɛ are consistent with the Knight relation and the voltage generator at the magnetopause boundary in the afternoon open R1. Near noon, the response of J// to Vsw is higher for southward than northward IMF. This can be attributed to the higher velocity shear at the magnetopause boundary due to higher sunward convection in the LLBL inside the magnetopause. R1 in the closed-field lines near dawn and dusk appear to be more sensitive to merging rate than to SW dynamic pressure.