Regions of ion energization observed during the Galaxy‐15 substorm with TWINS

Abstract

AbstractIons in the plasma sheet are measured by the energetic neutral atom imagers on the Two Wide‐Angle Imaging Neutral‐Atom Spectrometers (TWINS) spacecraft. A line of sight (LOS) projection is used to determine the location of the ions that dominate the measured spectrum, assuming that the equatorial plane is the hottest region along the LOS. We verify reasonable agreement between ion spectral shapes measured using this remote measurement technique and in situ measurements from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft during two moderate geomagnetic storms. Conditions for reliable use of this technique to determine ion spectra and effective ion temperatures are identified. The technique is applied to the substorm interval associated with the loss of communication with the Galaxy‐15 satellite. During this interval, localized and broad regions of ion energization are observed, demonstrating that magnetic reconnection and current disruption may have played a role during this very extreme event. These observations demonstrate the ability of this technique to cast local ion spectra measurements in a global context.