Wave-induced loss of ultra-relativistic electrons in the Van Allen radiation belts

Abstract

The dipole configuration of the Earth's magnetic field allows for the trapping of highly energetic particles, which form the radiation belts. Although significant advances have been made in understanding the acceleration mechanisms in the radiation belts, the loss processes remain poorly understood. Unique observations on 17 January 2013 provide detailed information throughout the belts on the energy spectrum and pitch angle (angle between the velocity of a particle and the magnetic field) distribution of electrons up to ultra-relativistic energies. Here we show that although relativistic electrons are enhanced, ultra-relativistic electrons become depleted and distributions of particles show very clear telltale signatures of electromagnetic ion cyclotron wave-induced loss. Comparisons between observations and modelling of the evolution of the electron flux and pitch angle show that electromagnetic ion cyclotron waves provide the dominant loss mechanism at ultra-relativistic energies and produce a profound dropout of the ultra-relativistic radiation belt fluxes.

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).…”

Rapid Loss of Radiation Belt Relativistic Electrons by EMIC Waves

“…There have been two main competing paradigms for the loss of radiation belt relativistic electrons: radial loss to the magnetopause (Shprits, Thorne, Friedel, et al, ; Loto'Aniu et al, ) and local loss to the atmosphere (Thorne & Kennel, ; Horne & Thorne, ; Summers et al, ). For the former, the primary observational evidence is the radially peaked PSD profile of relativistic electrons (Turner et al, ; Mann et al, ); for the latter, the observational evidences frequently mentioned in previous works are the wave‐related electron precipitation at low altitudes (Lorentzen et al, ; Millan et al, ; Miyoshi et al, ; Tsurutani et al, ; Breneman et al, ) and the flat‐top PAD characteristic (Usanova et al, ; Engebretson et al, ; Su et al, ; Shprits et al, ). Here on the basis of the analysis of an extreme radiation belt electron loss event observed by RBSP and POES on 27 February 2014, we present new evidence for the EMIC wave‐driven local precipitation loss of relativistic electrons in the heart of the outer radiation belt: The RBSP‐observed radial profile of the relativistic electron PSD appeared to be quasi‐monotonic, in contrast to the peaked type of previously reported events (e.g., Turner et al, ; Mann et al, ).…”

“…Wave‐driven pitch angle scattering can reduce the altitudes of electron mirror points, and collisions with atmospheric particles yield the precipitation loss of electrons. The primary characteristic of radial loss is a radially peaked PSD profile (Turner et al, ; Mann et al, ), while the main evidences for local loss are the flat‐top PAD characteristic (Usanova et al, ; Engebretson et al, ; Su et al, ; Shprits et al, ) and the wave‐related electron precipitation observed at low altitudes (Lorentzen et al, ; Millan et al, ; Miyoshi et al, ; Tsurutani et al, ; Breneman et al, ; Zhang, Halford, et al, ).…”

Merging fluxgate and induction coil data to produce low-noise geomagnetic observatory data meeting the INTERMAGNET definitive 1 s data standard

“…Obviously we have more than three conditional equations at hand and a solution must be found in the sense of minimizing the mean square of the residuals. The so-called normal equations (Schmucker and Weidelt, 1975) …”

“…Electrons interacting with such waves can be scattered into the loss cone and reduce the energy content of the radiation belt. Pc-1 pulsations (f > 0.1 Hz) can be caused by electromagnetic ion cyclotron (EMIC) waves, which is the subject of many recent investigations (e.g., Shprits et al, 2016or Usanova et al, 2014.…”