Multi‐MeV electron loss in the heart of the radiation belts

Abstract

Significant progress has been made in recent years in understanding acceleration mechanisms in the Earth's radiation belts. In particular, a number of studies demonstrated the importance of the local acceleration by analyzing the radial profiles of phase space density (PSD) and observing building up peaks in PSD. In this study, we focus on understanding of the local loss using very similar tools. The profiles of PSD for various values of the first adiabatic invariants during the previously studied 17 January 2013 storm are presented and discussed. The profiles of PSD show clear deepening minimums consistent with the scattering by electromagnetic ion cyclotron waves. Long‐term evolution shows that local minimums in PSD can persist for relatively long times. During considered interval of time the deepening minimums were observed around L* = 4 during 17 January 2013 storm and around L* = 3.5 during 1 March 2013 storm. This study shows a new method that can help identify the location, magnitude, and time of the local loss and will help quantify local loss in the future. This study also provides additional clear and definitive evidence that local loss plays a major role for the dynamics of the multi‐MeV electrons.

Signatures of Ultrarelativistic Electron Loss in the Heart of the Outer Radiation Belt Measured by Van Allen Probes

“…The duration of EMIC waves can be estimated from electron flux observations (converted to PSD) in case of deepening minimums as was discussed by Shprits et al (). The deepening minimum in ultrarelativistic electron PSD profiles indicates that local loss induced by EMIC waves dominates over the acceleration process driven by radial diffusion that tends to smooth out the minimum.…”

“…The simultaneous formation of local minimums in ultrarelativistic electron PSD profiles at L ∗ = 4.7, the decrease between L ∗ = 4.5 and 5, and slight changes at L ∗ = 5.5 imply a fast local loss process operating in a narrow region of L shells. The observed minimums could not be produced by magnetopause shadowing or by the local interaction with hiss or chorus waves, which is effective on the much longer time scales than the Van Allen Probe orbital period and characterized by a very weak dependence on radial distance (Orlova & Shprits, ; Orlova et al, ; Shprits et al, ). EMIC waves, resonating with ultrarelativistic electrons, can locally scatter electrons into the loss cone and form the minimums, as presented in Figures b and c.…”

Understanding the Mechanisms of Radiation Belt Dropouts Observed by Van Allen Probes

“…These local minima of PSD already existed before the dropout in profiles #1 and #2 but were deepened during the dropout. Recently, Shprits et al () suggested that the presence of deepening local minimums in the heart of outer radiation belt can be a signature of localized loss due to EMIC waves. We agree with their conclusions for the importance of EMIC wave scattering at low L * regions (~ L * < 4.2) for this event but would like to emphasize that additional loss mechanism may be required to explain the fast loss at large L * (~ L * > 4.2).…”

Identifying Radiation Belt Electron Source and Loss Processes by Assimilating Spacecraft Data in a Three‐Dimensional Diffusion Model

“…Their relevance to the radiation belt dynamics has been evaluated in earlier works, based either on observations or model simulations (Albert & Young, 2005;Albert et al, 2009;Drozdov et al, 2015Drozdov et al, , 2017Shprits et al, 2006Shprits et al, , 2008Shprits et al, , 2016Shprits et al, , 2017Subbotin et al, 2010;Turner, Angelopoulos, Morley, et al, 2014;Usanova et al, 2014;Xiang et al, 2017;Xiao et al, 2010;Yu et al, 2013). Their relevance to the radiation belt dynamics has been evaluated in earlier works, based either on observations or model simulations (Albert & Young, 2005;Albert et al, 2009;Drozdov et al, 2015Drozdov et al, , 2017Shprits et al, 2006Shprits et al, , 2008Shprits et al, , 2016Shprits et al, , 2017Subbotin et al, 2010;Turner, Angelopoulos, Morley, et al, 2014;Usanova et al, 2014;Xiang et al, 2017;Xiao et al, 2010;Yu et al, 2013).…”