Quantitative studies of terrestrial plasmaspheric dynamics enabled by the IMAGE spacecraft

Abstract

Terrestrial plasmaspheric dynamics have been observed using single satellite passes and long term statistical studies for many years all with in-situ measurements. The EUV instrument aboard the IMAGE spacecraft provided global plasmaspheric data by imaging He-II at 30.4nm. The global imaging revealed significant dynamics modifying current theory and observing many new features. Global imaging removes any space/time ambiguity and provides a regular high-quality data set ideal for correlative studies and region comparisons. This work presents several studies enabled by this global imaging: an empirical model of plasmapause position as a function of solar wind parameters, a derivation of the global magnetospheric convection electric field based on plasmaspheric feature tracking, and a study of plasmaspheric rotation and its associated ionospheric ion drift signature. Using plasmapause position data extracted from inverted EUV images, the plasmapause position is found to be strongly correlated with the interplanetary magnetic field (IMF) z-component and a magnetospheric merging proxy.

Delay in the plasmapause response to the arrival of solar wind conditions at Earth is found to be 180 minutes for the IMF z-component while the delay from the arrival of the merging proxy is found to be 240 minutes. This result allows an upstream solar wind monitor such as ACE to enable a simple prediction of the plasmapause location three hours in advance. Using inverted IMAGE-EUV data it is demonstrated that Alfvén layer boundary positions are sufficient to derive the magnetospheric convection electric field strength. This result provides a global imaging method to derive a parameter responsible for significant inner magnetospheric dynamics. No ionospheric drift differences are found between corotating and sub-corotating plasmaspheric conditions; this is believed to be caused by an under-sampling in the drift measurement locations, highlighting the need for further exploration of magnetosphere-ionosphere (M-I) coupling.