Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

Abstract

Abstract. Energetic radiation belt electron fluxes can undergo sudden dropouts in response to different solar wind drivers. Many physical processes contribute to the electron flux dropout, but their respective roles in the net electron depletion remain a fundamental puzzle. Some previous studies have qualitatively examined the importance of magnetopause shadowing in the sudden dropouts either from observations or from simulations. While it is difficult to directly measure the electron flux loss into the solar wind, radial diffusion codes with a fixed boundary location (commonly utilized in the literature) are not able to explicitly account for magnetopause shadowing. The exact percentage of its contribution has therefore not yet been resolved. To overcome these limitations and to determine the exact contribution in percentage, we carry out radial diffusion simulations with the magnetopause shadowing effect explicitly accounted for during a superposed solar wind stream interface passage, and quantify the relative contribution of the magnetopause shadowing coupled with outward radial diffusion by comparing with GPS-observed total flux dropout. Results indicate that during high-speed solar wind stream events, which are typically preceded by enhanced dynamic pressure and hence a compressed magnetosphere, magnetopause shadowing coupled with the outward radial diffusion can explain about 60-99 % of the main-phase radiation belt electron depletion near the geosynchronous orbit. While the outer region (L * > 5) can nearly be explained by the above coupled mechanism, additional loss mechanisms are needed to fully explain the energetic electron loss for the inner region (L * ≤ 5). While this conclusion confirms earlier studies, our quantification study demonstrates its relative importance with respect to other mechanisms at different locations.

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

“…Nevertheless, quantitative assessments of the contribution of each process have been scarce (Yu et al, 2013). Nevertheless, quantitative assessments of the contribution of each process have been scarce (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). 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).…”

Extreme geomagnetic disturbances due to shocks within CMEs

“…This occurred because of the simultaneous jump in dynamic pressure and southward B z , the latter eroding the dayside magnetosphere. GOES 8 measured a large drop of the flux of energetic electrons at geosynchronous orbit which stopped with the end of the compressed CME, consistent with magnetopause shadowing [ Yu et al , ].…”

Time‐Integral Correlations of Multiple Variables With the Relativistic‐Electron Flux at Geosynchronous Orbit: The Strong Roles of Substorm‐Injected Electrons and the Ion Plasma Sheet

“…The sign of the correlation of d mp with F e1.2 for this physical process should be positive, with more radiation‐belt loss when d mp is smaller (cf. Table ). Enhanced ULF wave‐driven radial diffusion is thought to act in concert with magnetopause shadowing to transport radiation‐belt electrons outward to the magnetopause to be lost (e.g., Ozeke et al, ; Shprits et al, ; Yu, Koller, & Morley, ). A controlling variable for this processes is S geo , the amplitude of ULF fluctuations at geosynchronous orbit.…”