Relativistic electron response to the combined magnetospheric impact of a coronal mass ejection overlapping with a high‐speed stream: Van Allen Probes observations

Abstract

During early November 2013, the magnetosphere experienced concurrent driving by a coronal mass ejection (CME) during an ongoing high‐speed stream (HSS) event. The relativistic electron response to these two kinds of drivers, i.e., HSS and CME, is typically different, with the former often leading to a slower buildup of electrons at larger radial distances, while the latter energizing electrons rapidly with flux enhancements occurring closer to the Earth. We present a detailed analysis of the relativistic electron response including radial profiles of phase space density as observed by both Magnetic Electron and Ion Sensor (MagEIS) and Relativistic Electron Proton Telescope instruments on the Van Allen Probes mission. Data from the MagEIS instrument establish the behavior of lower energy (<1 MeV) electrons which span both intermediary and seed populations during electron energization. Measurements characterizing the plasma waves and magnetospheric electric and magnetic fields during this period are obtained by the Electric and Magnetic Field Instrument Suite and Integrated Science instrument on board Van Allen Probes, Search Coil Magnetometer and Flux Gate Magnetometer instruments on board Time History of Events and Macroscale Interactions during Substorms, and the low‐altitude Polar‐orbiting Operational Environmental Satellites. These observations suggest that during this time period, both radial transport and local in situ processes are involved in the energization of electrons. The energization attributable to radial diffusion is most clearly evident for the lower energy (<1 MeV) electrons, while the effects of in situ energization by interaction of chorus waves are prominent in the higher‐energy electrons.

Current energetic particle sensors

“…Figures a–d show an example electron spectrum taken following a magnetic storm [ Kanekal et al ., ]. These show a peak in the phase space density radial profiles formed over a range of first invariant values (Figures c and d), similar to those from Reeves et al .…”

“…This background correction capability was used to make new measurements of the electron fluxes and spectra in the inner radiation zone [ Fennell et al ., ] and to produce data free from Bremsstrahlung for multiple storm time studies such as those by Kanekal et al . [], Jaynes et al . [], Turner et al .…”

“…Histogram data are used to correct the Main Channel data for penetrating background as indicated in Figure 3 [see Claudepierre et al, 2013Claudepierre et al, , 2015. This background correction capability was used to make new Journal of Geophysical Research: Space Physics 10.1002/2016JA022588 measurements of the electron fluxes and spectra in the inner radiation zone [Fennell et al, 2014b] and to produce data free from Bremsstrahlung for multiple storm time studies such as those by Kanekal et al [2015], Jaynes et al [2015], Turner et al [2015], and others. Figure 10e, which is discussed later, shows electron spectra at L = 1.5 determined by MagEIS using the background-corrected data.…”

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

“…Although energetic electron injections during substorms or enhanced convection provide seed electrons (from tens of keV to hundreds of keV) [ Miyoshi et al ., ; Baker and Kanekal , ; Thorne , ; Boyd et al ., ; Dai et al ., ; Jaynes et al ., ], this process is unlikely to directly lead to the net electron acceleration up to multiple MeV. Inward radial diffusion caused by interaction with Ultra‐Low‐Frequency (ULF) waves can accelerate electrons to higher energies [ Hudson et al ., ; Mathie and Mann , ; Perry et al ., ; Ukhorskiy et al ., ], but this process alone is unlikely to account for the observed outer radiation belt electron dynamics which often exhibits growing radial peaks in electron phase space density (PSD) at ultrarelativistic energies in the heart of the radiation belts [ Green and Kivelson , ; Iles et al ., ; Chen et al ., ; Turner et al ., ; Reeves et al ., ; Thorne et al ., ; Kanekal et al ., ]. This suggests that an internal heating process is operating, and the potential candidates for this local acceleration include energy diffusion by chorus and magnetosonic (MS) waves [e.g., Summers et al ., ; Horne et al ., , , ; Thorne et al ., ; Ma et al ., ].…”

“…Regarding how electrons are accelerated to ultrarelativistic energies in the radiation belts, several mechanisms have been considered to be potentially important. Although energetic electron injections during substorms or enhanced convection provide seed electrons (from tens of keV to hundreds of keV) [Miyoshi et al, 2003;Baker and Kanekal, 2008;Thorne, 2010;Boyd et al, 2014;Dai et al, 2014;Jaynes et al, higher energies [Hudson et al, 1999;Mathie and Mann, 2000;Perry et al, 2005;Ukhorskiy et al, 2009], but this process alone is unlikely to account for the observed outer radiation belt electron dynamics which often exhibits growing radial peaks in electron phase space density (PSD) at ultrarelativistic energies in the heart of the radiation belts [Green and Kivelson, 2004;Iles et al, 2006;Chen et al, 2007;Turner et al, 2014;Reeves et al, 2013;Thorne et al, 2013a;Kanekal et al, 2015]. This suggests that an internal heating process is operating, and the potential candidates for this local acceleration include energy diffusion by chorus and magnetosonic (MS) waves [e.g., Summers et al, 2002;Horne et al, 2005aHorne et al, , 2005bHorne et al, , 2007Thorne et al, 2013a;Ma et al, 2016].…”