EMIC‐Wave Driven Electron Precipitation Observed by CALET on the International Space Station. Issue 6 (15th March 2022)

• Record Type: Journal Article
• Authors: Bruno, A.; Blum, L. W.; de Nolfo, G. A.; Kataoka, R.; Torii, S.; Greeley, A. D.; Kanekal, S. G.; Ficklin, A. W.; Guzik, T. G.; Nakahira, S.
• Is Part Of: Geophysical research letters. Volume 49:Issue 6(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-03-15
• Subjects: radiation belts -- relativistic electron precipitation -- EMIC waves; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL097529
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We present an analysis of the relativistic electron precipitation (REP) event measured by the CALorimetric Electron Telescope (CALET) experiment on board the International Space Station during a relatively weak geomagnetic storm on 31 December 2016. CALET observations were compared with the measurements of the Van Allen Probes in the near‐equatorial plane to investigate the global radiation belt dynamics and the REP drivers. The magnetically conjugate observations from these two missions demonstrate that the significant MeV precipitation directly detected by CALET in low‐Earth orbit during a period of radiation belt depletion following the passage of a high‐speed stream, was associated with dusk‐side electromagnetic ion cyclotron (EMIC) waves. In addition, the combined wave, REP and trapped electron data suggest that the reported radiation belt depletion can be likely ascribed to the concomitant loss effects of EMIC wave scattering driving the atmospheric precipitation, as well as outward radial diffusion associated with magnetopause shadowing. Plain Language Summary: Relativistic electron precipitation (REP) is a space‐weather phenomenon commonly observed at high latitudes, in which energetic electrons trapped in the geomagnetic field are lost into the Earth's atmosphere. Along with outward radial diffusion associated with magnetopause shadowing, it represents the primary loss mechanism for the outer radiation belt. While previous studies have demonstrated that REP can be caused by scattering with electromagnetic ion cyclotron (EMIC) waves, a direct contribution of this process to belt depletion events is still debated. In this work, we examine a dropout event that occurred on 31 December 2016, comparing the REP observations of the CALorimetric Electron Telescope (CALET) on the International Space Station, with the magnetically conjugate wave measurements of the Van Allen Probes in the near‐equatorial plane. The analysis of combined data demonstrates that the REP event detected by CALET was likely driven by EMIC waves, and that the observed radiation belt depletion can be attributed to the concomitant loss effects of EMIC wave scattering and magnetopause shadowing. Key Points: We present a study of relativistic electron precipitation into the atmosphere with CALorimetric Electron Telescope on the International Space Station during a radiation belt depletion event The magnetically conjugate measurements with the Van Allen Probes show that the observed precipitation was driven by dusk‐side electromagnetic ion cyclotron waves Combined wave and particle data suggest that the radiation belt flux dropout was caused by both wave scattering and outward losses