Solar wind driving of dayside field-aligned currents

Variations in the dayside field-aligned current (FAC) density (J(//)), field-aligned parallel potential drop (Delta phi(//)), peak precipitating electron energy (peak E-e), and precipitating electron energy flux (epsilon) as functions of solar wind (SW) and interplanetary magnetic field (IMF) are investigated with Defense Meteorological Satellite Program observations and a quasi-stationary low-latitude boundary layer (LLBL)-FAC coupling model. Region 1 (R1) J(//) responses to variations in SW velocity (V-sw) and density (n(sw)) at 8-16 magnetic local time (MLT) suggest that R1 at these local times is frequently open while R1 at 6-08 and 17-18 MLT is frequently closed. R2 is located mostly on closed field lines. In the afternoon open R1 at 12-16 MLT, an increase in n(sw) increases J(//), decreases maximum peak Ee (proxy for Delta phi(//)), but has little effect on maximum epsilon. In the same R1 region, an increase in V-sw increases J(//), maximum peak E-e, and maximum epsilon. The dependencies of J(//), maximum peak E-e, and maximum epsilon are consistent with the Knight relation and the voltage generator at the magnetopause boundary in the afternoon open R1. In the midmorning and midafternoon, the response of J(//) to V-sw is higher for southward than for 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 appears to be more sensitive to merging rate (d Phi/dt = V-4/3(sw) B-T(2/3) sin(8/3)(theta(c)/2)) than to SW dynamic pressure.