Imaging Earth's plasmasphere at 30.4nm

Abstract

Extreme Ultraviolet (EUV) imaging has the strong potential to provide the global observations needed to tie together the numerous in situ measurements made by a host of Earth orbiting satellites. First, EUV imaging can capture the dayside solar wind magnetosphere (SWM) interaction that defines the energy input to the system. As the solar wind encounters the dayside magnetopause (see Figure 1), charge exchange between solar wind α particles (He ions) and the neutral exosphere produces a 30.4 nm emission that ranges from 0.25 milliRayleighs (during nominal conditions) to 6 Rayleighs (during disturbed conditions). We know that this solar wind energy input carries field lines over the polar caps to the nightside, where explosive substorms produce an earthward (or sunward) return flow that erodes the plasmasphere, causing the formation of sunward-pointing dayside plumes. These plumes can transport away 30-100 tons of magnetospheric plasma (approximately 20-40% of the initial He distribution) in just a few hours. The Extreme Ultraviolet Imager aboard NASA's Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) captured the erosion process with 10-minute resolution. An improved EUV imager that could capture erosion with 1-minute time resolution would answer many outstanding questions about the mechanics of the removal of so much plasma. Secondly, theoretical models and some observations suggest that the arrival of tons of dense plasma at the magnetopause may reduce or suppress the solar wind energy input; i.e., feedback from the magnetosphere can squelch the SWM interaction. Finally, we know from the IMAGE mission that EUV filtered imaging also captures the Far Ultraviolet (FUV) aurora, which is a measure of the overall time-dependent strength of the SWM interaction.