Observations and modeling of energetic electron dynamics during the October 2001 storm

Abstract

[1] We examined and simulated the dynamics of energetic electrons during the October 2001 magnetic storm with the relativistic RAM electron model for a wide range of energies. The storm had a rapid main phase followed by a day of strong geomagnetic activity that produced a second Dst minimum and then a very quiet recovery phase. During the main phase and the period of intense activity, the observed hot electron flux (E = 30 keV) increased at low L while decreasing at large L and then decayed abruptly at the beginning of the recovery phase when activity subsided. The flux of subrelativistic (E = 100-300 keV) electrons also increased at low L and decreased at large L during the main phase and the period of intense activity but remained high throughout the recovery phase. In contrast, the relativistic (E = 300-1200 keV) electron flux decreased during the main phase, remained low throughout the period of intense activity, and then increased above prestorm values during the recovery phase in spite of the low activity. The highest energy electron flux (E > 1200 keV) decreased during the main phase and never recovered to prestorm levels. The numerical simulation was compared with observations. We identified the physical processes which produce the flux variations at the different energies. In the simulation, the hot electrons were convected inward during the main phase, reproducing the observed local time flux asymmetry. The higher-energy electrons, on the other hand, were predominantly transported inward by radial diffusion and not convective motion. The simulation was not able to reproduce the subrelativistic and relativistic electron flux enhancement and spatial expansion as observed during the recovery phase. In the simulation, most of the energization occurred around the main phase and the period of intense activity with negligible transport or flux enhancement during the recovery phase. The discrepancy between the observed and simulated high energy electron flux suggests that only convective transport and radial diffusion cannot fully explain the electron dynamics. An additional mechanism may be necessary to explain enhancements of high energy electron flux during the recovery phase of the storm.

Space Weather Effects Produced by the Ring Current Particles

“…Occurrence of a storm, even a moderate one, can be not directly related to the occurrence of the surface charging. The electron flux at the keV energies is largely determined by convective (Korth et al 1999;Elkington et al 2004;Miyoshi et al 2006;Kurita et al 2011;) and substorm-associated (Vakulin et al 1988;Grafodatskiy et al 1987;Degtyarev et al 1990;Fok et al 2001a;Khazanov et al 2004;Kozelova et al 2006;Ganushkina et al 2013;Turner et al 2015) electric fields. Since it varies on short time scales, it is not possible to average the keV electron fluxes over an orbit/day/hour as it can be done for higher energies, like MeVs.…”

The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on RBSP

“…The properties of magnetospheric ULF waves, excited in response to solar wind variability, have also been obtained from global MHD simulations and used to study the dynamic variability of radiation belt electrons (Fei et al 2006;Kress et al 2007). Although radial diffusion transport is able to simulate several important features of radiation belt dynamics, it fails to describe the rapid flux variation and the prolonged duration of electron acceleration observed during individual storms (Miyoshi et al 2001;). The ability of ULF waves to cause effective radial diffusion depends on the amplitude and the poloidal or toroidal properties of the waves and their modal structure (Perry et al 2005).…”

“…Since the power in ULF waves is considerably enhanced during magnetic storms (Mathie and Mann 2000), radial diffusion is a potentially important mechanism for energetic electron acceleration (Rostoker et al 1998;Elkington et al 1999;Hudson et al 2001;O'Brien et al 2001;Shprits and Thorne 2004) or loss (Shprits et al 2006;Jordanova et al 2008;) during storm conditions, dependent on the radial gradient in phase space density. Higher frequency ELF and VLF waves cause violation of the first two invariants and lead to pitch angle scattering loss to the atmosphere (Thorne and Kennel 1971;Lyons et al 1972;Thorne 1998a, 1998b) or local stochastic energy diffusion (Horne and Thorne 1998;Summers et al 1998;Miyoshi et al 2003).…”

On the cause and extent of outer radiation belt losses during the 30 September 2012 dropout event

“…Losses can extend to L* lower than those directly affected by the magnetopause shadowing due to a rapid cascade of outward radial transport that can occur if the distinct PSD radial distribution remaining after magnetopause shadowing is perturbed by wave activity that violates the third invariant [e.g., Shprits et al, 2006;Miyoshi et al, 2006;Loto'aniu et al, 2010;Turner et al, 2012a]. However, arguments have been made against this mechanism based on energetic ring current ions not observed to undergo similar behavior concurrently [i.e., Green et al, 2004], since magnetopause shadowing and subsequent outward transport should affect trapped energetic ring current ions much like the electrons.…”