Numerical experiments on the inner magnetospheric electric field

Abstract

Inner magnetospheric electric fields are often complicated by a reduction of the total electric field at low‐latitudes called shielding and an intensification of the electric field equatorward of the auroral oval called a subauroral polarization stream (SAPS). To better understand the stormtime behavior of these electric fields, computer experiments have been conducted using the Rice Convection Model (RCM). The RCM computes the Region‐2 Birkeland currents and the inner magnetospheric electric field and particle distribution. It uses as input a magnetic field and the plasma sheet pressure and energy distribution and assumes that particle loss is negligible. The base or control run used realistic model inputs, while the experiments varied fundamental model inputs to test the electric field's sensitivity to magnetospheric conditions. The first experiment is a high‐pressure or dense plasma sheet run, where the boundary density and pressure are a factor of three higher than in the base run. The high‐pressure run produced better shielding and a stronger SAPS. The second experiment is a cold plasma sheet run in which the plasma sheet temperature was reduced by a factor of thirty, while the pressure remained constant. In this run, the gradient and curvature drift is small compared with the × drift. With particle transport similar to ideal MHD, the cold plasma sheet run produced excellent shielding and strong Region‐2 currents. This is in contrast to the weak shielding and Region‐2 currents produced by global MHD codes. In addition, the SAPS feature is significantly strengthened. The final experiment held the magnetic field constant. This run produced marginally better shielding. However, the magnetospheric signature of SAPS is very weak, suggesting that magnetic field variations are important in SAPS formation.