On the Variability of EMIC Waves and the Consequences for the Relativistic Electron Radiation Belt Population

Abstract

The outer electron radiation belt is highly variable with electron energies reaching up to well over several MeV (Baker et al., 2012). Their behavior is governed by a range of physical processes that when combined give rise to complex spatial and temporal behavior. Whistler mode chorus waves (

Depletions of Multi‐MeV Electrons and Their Association to Minima in Phase Space Density

“…The large percentage of depletion events that are associated with PSD minima indicates that, very often, the depletion of the multi-MeV electron radiation belts is linked to fast localized loss processes originating from EMIC wave activity, consistent with previous results (e.g., Cervantes, Shprits, Aseev, & Allison, 2020;Ross et al, 2021;Xiang et al, 2018).…”

The Importance of Ion Composition for Radiation Belt Modeling

“…In this work, we made use of the hydrogen and helium band EMIC waves that were identified in Ross et al. (2021). The EMIC wave spectra were determined from the 64 Hz magnetometer data from the EMFISIS instrument (Kletzing et al., 2013) on board Van Allen Probe A over the duration of the mission (Mauk et al., 2013).…”

“…In addition to the ion composition, E min depends on the ratio of the wave frequency to proton gyrofrequency, f/f cp , and the plasma frequency to electron gyrofrequency ratio, f pe / f ce . For illustration, for both hydrogen and helium band EMIC waves, we adopted the 80th percentile for the EMIC wave frequency to proton gyrofrequency ratio from Ross et al (2021) because the high-frequency EMIC waves have the most significant contribution to radiation belt electrons with energies of several MeV.…”

“…Ross et al. (2021) showed that 80% of hydrogen band waves are in regions with densities less than average plasmaspheric values and therefore will infrequently interact with ∼2 MeV electrons.…”

Electron Diffusion by Magnetosonic Waves in the Earth’s Radiation Belts

“…The importance of capturing the variability of f pe /f ce in chorus acceleration of MeV electrons was shown in Agapitov et al (2019), where analytical estimates of bounce-averaged MeV electron diffusion rates were computed using local f pe /f ce values and mean wave spectra. More recent studies have shown that it is important to include both the variability of the wave spectra and the plasma properties in radiation belt modeling (Agapitov et al, 2020;Ross et al, 2020Ross et al, , 2021Watt et al, 2019). Watt et al (2019) showed that the mean pitch angle diffusion coefficients, D αα , for plasmaspheric hiss calculated by averaging the D αα from colocated and simultaneous measurements of the wave power and f pe /f ce were larger than those calculated from average values of the wave power and f pe /f ce .…”