Long‐Term Variations of Quasi‐Trapped and Trapped Electrons in the Inner Radiation Belt Observed by DEMETER and SAMPEX

• Published in: Journal of geophysical research. Space physics 2020-09, Vol.125 (9), p.n/a
• Main Authors: Zhang, Kun, Li, Xinlin, Xiang, Zheng, Khoo, Leng Ying, Zhao, Hong, Looper, Mark D., Temerin, Michael A., Sauvaud, Jean‐André
• Format: Article
• Language: English
• Subjects: Albedo; Correlation coefficient; Correlation coefficients; Cosmic ray albedo; Cosmic ray intensities; Cosmic rays; CRAND; Decay; Earthquakes; Electron density; Electron flux; Explorer satellites; geomagnetic storm; Geomagnetic storms; Geomagnetism; inner belt; Inner radiation belt; Magnetic storms; Magnetospheres; Neutron decay; Neutron flux; Pitch (inclination); quasi‐trapped; Radiation; radiation belt electron; Radiation belts; Seismic activity; Solar cycle; Solar maximum; Solar minimum; Sunspot cycle; Sunspot numbers; Sunspots; trapped; Trapped electrons
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2020JA028086

Electrons in the Earth's radiation belts can be categorized into three populations: precipitating, quasi‐trapped, and trapped. We use data from the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and Solar, Anomalous, and Magnetospheric Particle Explorer satellite (SAMPEX) missions and from ground‐based neutron monitors (NM) and sunspot observations to investigate the long‐term variation of quasi‐trapped and trapped sub‐MeV electrons on different L shells in the inner belt. DEMETER and SAMPEX measurements span over 17 years and show that at L ≤ 1.14 the electron flux is anticorrelated with sunspot number, but proportional to the cosmic ray intensity represented by NM count rates, which suggests that electrons at the inner edge of the inner belt are produced by Cosmic Ray Albedo Neutron Decay (CRAND). The solar cycle variation of cosmic rays increased the electron flux at L ≤ 1.14 by a factor of 2 from solar maximum at 2001 to solar minimum at 2009. At L ≥ 1.2, both quasi‐trapped and trapped electrons are enhanced during geomagnetic storms and decay to a background level during extended quiet times. At L > 2, quasi‐trapped electrons resemble trapped electrons, with correlation coefficients as high as 0.97, indicating that pitch angle scattering is the dominant process in this region. Key Points Sub‐MeV electrons at L ≤ 1.14 are anticorrelated with sunspot number suggesting their source to be Cosmic Ray Albedo Neutron Decay Electrons at L ≥ 1.2 are enhanced during large geomagnetic storms and decay to a background level during extended quiet times Quasi‐trapped electrons at L > 2 are highly correlated with trapped electrons, indicating that pitch angle scattering dominates