SC-Associated Electric Field Variations in the Magnetosphere and Ionospheric Convective Flows

Abstract

We examine magnetic and electric field perturbations associated with a sudden commencement (SC), caused by and interplanetary (IP) shock passing over the Earth's magnetosphere on 16 February 2013. The SC was identified in the magnetic and elecric data measured at THEMIS-E, Van Allen Probe-A, and Van Allen Probe-B in the magnetosphere. During the SC interval, THE-E observed a dawnward-then-duskward electric (E) field perturbation atround noon, while VAP-B observed a duskward E-field perturbation atround midnight. VAP-A observed a dawnward-then-duskward E-field perturbation in the postmidnight sector, but the duration and magnitude of the dawnward E-perturbation are much shorter and waker than that of THE-E. That is, the E-field signature changes with local time during the SC interval. The SuperDARN radar indicate that the ionospheric plasma motions during the SC are mainly due to the E-field variations observed in space. This indicates that the SC-associated E-field in space plays a significant role in determining the dynamic variations of the ionospheric convection flow. By comparing previous SC MHD simulations and our observations, we suggest that the E-field variations observed at the spacecraft are produced by magnetospheric convection flows due to deformation of the magnetosphere as the IP shock sweeps the magnetopause.