Radiation belt electron acceleration during the 17 March 2015 geomagnetic storm: Observations and simulations

Abstract

Various physical processes are known to cause acceleration, loss, and transport of energetic electrons in the Earth's radiation belts, but their quantitative roles in different time and space need further investigation. During the largest storm over the past decade (17 March 2015), relativistic electrons experienced fairly rapid acceleration up to ~7 MeV within 2 days after an initial substantial dropout, as observed by Van Allen Probes. In the present paper, we evaluate the relative roles of various physical processes during the recovery phase of this large storm using a 3‐D diffusion simulation. By quantitatively comparing the observed and simulated electron evolution, we found that chorus plays a critical role in accelerating electrons up to several MeV near the developing peak location and produces characteristic flat‐top pitch angle distributions. By only including radial diffusion, the simulation underestimates the observed electron acceleration, while radial diffusion plays an important role in redistributing electrons and potentially accelerates them to even higher energies. Moreover, plasmaspheric hiss is found to provide efficient pitch angle scattering losses for hundreds of keV electrons, while its scattering effect on > 1 MeV electrons is relatively slow. Although an additional loss process is required to fully explain the overestimated electron fluxes at multi‐MeV, the combined physical processes of radial diffusion and pitch angle and energy diffusion by chorus and hiss reproduce the observed electron dynamics remarkably well, suggesting that quasi‐linear diffusion theory is reasonable to evaluate radiation belt electron dynamics during this big storm.

On the Close Correspondence Between Storm Time ULF Wave Power and the POES VLF Chorus Wave Amplitude Proxy

“…One such mechanism has been proposed by Rae et al (2018), whereby localized compressional ULF waves modulate the loss cone, bringing it within reach of a wider range of equatorial pitch angles for energetic particles. That is not to say that chorus waves do not exist during some times when precipitation is observed by POES; indeed, satellite measurements have, on several occasions, shown chorus waves in correlation with those inferred using the precipitation VLF proxy (Li et al, , 2016). Indeed, the nature of storm time ULF waves (e.g., Anderson et al, 1990;Dai et al, 2015) that might be associated with precipitation is an important topic for future study.…”

Quantification of Energetic Electron Precipitation Driven by Plume Whistler Mode Waves, Plasmaspheric Hiss, and Exohiss

“…Summers et al (2008) found that hundreds of keV seed electron population, which can be further accelerated to MeV electrons (Horne et al, 2005;Thorne et al, 2013), is subject to rapid precipitation loss due to scattering by plume whistler mode waves, thus reducing the effect of MeV electron acceleration. In spite of the importance of plume whistler mode waves, it is crucial to note that the effects of plume whistler mode waves have not been accurately incorporated into most global radiation belt modeling yet (e.g., Albert et al, 2009;Glauert et al, 2014;Li et al, 2016;Ma et al, 2018;Tu et al, 2014). In spite of the importance of plume whistler mode waves, it is crucial to note that the effects of plume whistler mode waves have not been accurately incorporated into most global radiation belt modeling yet (e.g., Albert et al, 2009;Glauert et al, 2014;Li et al, 2016;Ma et al, 2018;Tu et al, 2014).…”

The effects of magnetospheric processes on relativistic electron dynamics in the Earth's outer radiation belt

“…Therefore, MeV electron PSDs at different L* were far more than prestorm values (Figures b–e) due to the local acceleration by chorus waves and radial diffusion [e.g., Baker et al ., ; W . Li et al ., ].…”