Multiyear Measurements of Radiation Belt Electrons: Acceleration, Transport, and Loss

Abstract

In addition to clarifying morphological structures of the Earth's radiation belts, it has also been a major achievement of the Van Allen Probes mission to understand more thoroughly how highly relativistic and ultrarelativistic electrons are accelerated deep inside the radiation belts. Prior studies have demonstrated that electrons up to energies of 10 megaelectron volts (MeV) can be produced over broad regions of the outer Van Allen zone on timescales of minutes to a few hours. It often is seen that geomagnetic activity driven by strong solar storms (i.e., coronal mass ejections, or CMEs) almost inexorably leads to relativistic electron production through the intermediary step of intense magnetospheric substorms. In this study, we report observations over the 6‐year period 1 September 2012 to 1 September 2018. We focus on data about the relativistic and ultrarelativistic electrons (E≥5 MeV) measured by the Relativistic Electron‐Proton Telescope sensors on board the Van Allen Probes spacecraft. This work portrays the radiation belt acceleration, transport, and loss characteristics over a wide range of geomagnetic events. We emphasize features seen repeatedly in the data (three‐belt structures, “impenetrable” barrier properties, and radial diffusion signatures) in the context of acceleration and loss mechanisms. We especially highlight solar wind forcing of the ultrarelativistic electron populations and extended periods when such electrons were absent. The analysis includes new display tools showing spatial features of the mission‐long time variability of the outer Van Allen belt emphasizing the remarkable dynamics of the system.

Forecasting Megaelectron‐Volt Electrons Inside Earth's Outer Radiation Belt: PreMevE 2.0 Based on Supervised Machine Learning Algorithms

“…The difference in performance can be explained by the fact that a much larger training set incorporate a wider flux variation that can be helpful to train the models. Besides, the addition of SW speeds definitely helps improve the performance of linear models at large L‐shells, which is consistent with Baker et al's study (Baker et al, ) that confirms the importance of solar wind speeds for MeV electron flux levels.…”

Statistical Dependence of EMIC Wave Scattering on Wave and Plasma Parameters

“…The initial trapped electron level varies for the year investigated. The trapped flux level is especially low in the year 2014 compared to other periods (Baker et al, ) when recurrent high‐speed solar wind streams that are favorable for accelerating electrons (Baker et al, ; Li et al, ; McPherron et al, ) are frequently observed. The number of conjunction events, coincidence events and coincidence occurrence rate for each year are shown in Table .…”

Sustaining Saturn's Electron Radiation Belts Through Episodic, Global‐Scale Relativistic Electron Flux Enhancements

“…The large number of the transient extensions indicates that they are caused by dynamic processes that are common for the Saturnian magnetosphere and are efficient in accelerating electrons to MeV energies. Note that the variability of Earth's electron belts is also very significant (e.g., Baker et al, ), even though the triggers might be different (Ma et al, ; Turner et al, ; Yuan & Zong, , ). Whereas, the proton belts of both planets are relatively less dynamic than their electron counterparts (Kollmann et al, ).…”