Multi-point Measurements of Relativistic Electrons in the Magnetosphere

Abstract:

The dynamic nature of relativistic electrons in the magnetosphere is well known but the detailed causes are not, partially due to the lack of a system-wide observation that would provide physical constraints for comprehensive modeling efforts. The Van Allen Probes, which are in a low inclination (10⁰) geo-transfer-like orbit, carry the state-of-art particle and field measurements. The Relativistic Electron and Proton Telescope (REPT) and the Magnetic Electron Ion Spectrometer (MagEIS) instruments aboard measure the full distribution of relativistic electrons as they traverse the heart of both inner and outer radiation belt. However, due to the small equatorial loss cone (only a few degrees at outer belt), it is difficult for REPT and MagEIS to directly determine which electrons will precipitate into the atmosphere and which ones will remain trapped in the outer radiation belt. The Relativistic Electron and Proton Telescope integrated little experiment (REPTile) onboard the Colorado Student Space Weather Experiment (CSSWE) CubeSat, which is in a highly inclined (65⁰) low Earth orbit, measures only the fraction of the total population that have small enough equatorial pitch angles to reach the altitude of CSSWE, thus measuring the precipitating population as well as the trapped population. Finally, the THEMIS spacecraft, because of their higher apogees, provide critical information of the electron source populations, which can be at beyond Van Allen Probes’ apogees.

In this presentation, coordinated measurements of the relativistic electrons from multiple spacecraft will be presented and conclusions will be drawn based on the measurement and preliminary modeling, including the upper limit of the relativistic electron population in the inner belt.