The Response of Earth's Electron Radiation Belts to Geomagnetic Storms: Statistics From the Van Allen Probes Era Including Effects From Different Storm Drivers

Abstract

A statistical study was conducted of Earth's radiation belt electron response to geomagnetic storms using NASA's Van Allen Probes mission. Data for electrons with energies ranging from 30 keV to 6.3 MeV were included and examined as a function of L‐shell, energy, and epoch time during 110 storms with SYM‐H ≤−50 nT during September 2012 to September 2017 (inclusive). The radiation belt response revealed clear energy and L‐shell dependencies, with tens of keV electrons enhanced at all L‐shells (2.5 ≤ L ≤ 6) in all storms during the storm commencement and main phase and then quickly decaying away during the early recovery phase, low hundreds of keV electrons enhanced at lower L‐shells (~3 ≤ L ≤ ~4) in upward of 90% of all storms and then decaying gradually during the recovery phase, and relativistic electrons throughout the outer belt showing main phase dropouts with subsequent and generally unpredictable levels of replenishment during the recovery phase. Compared to prestorm levels, electrons with energies >1 MeV also revealed a marked increase in likelihood of a depletion at all L‐shells through the outer belt (3.5 ≤ L ≤ 6). Additional statistics were compiled revealing the storm time morphology of the radiation belts, confirming the aforementioned qualitative behavior. Considering storm drivers in the solar wind: storms driven by coronal mass ejection (CME) shocks/sheaths and CME ejecta only are most likely to result in a depletion of >1‐MeV electrons throughout the outer belt, while storms driven by full CMEs and stream interaction regions are most likely to produce an enhancement of MeV electrons at lower (L < ~5) and higher (L > ~4.5) L‐shells, respectively. CME sheaths intriguingly result in a distinct enhancement of ~1‐MeV electrons around L~5.5, and on average, CME sheaths and stream interaction regions result in double outer belt structures.

Superposed Epoch Analysis of the Energetic Electron Flux Variations During CIRs Measured by BD‐IES

“…These results are consistent with previous research on the electron dropouts and the energy-dependent recovery process during CIRs (e.g., Morley et al, 2010;Shen et al, 2017;Turner et al, 2019). According to the results of superposed epoch analysis, we have shown that there does have a time sequence of energetic electron enhancements during CIRs.…”

Variation of Radiation Belt Electron Flux During CME‐ and CIR‐Driven Geomagnetic Storms: Van Allen Probes Observations

“…Here, we continue to develop and extend previous studies of the electron flux response by not only focusing on different energies but also different L-values (e.g., Turner et al, 2019). Here, we continue to develop and extend previous studies of the electron flux response by not only focusing on different energies but also different L-values (e.g., Turner et al, 2019).…”

“…The mechanisms responsible for the development of radiation belt electrons during CME-and CIR-driven geomagnetic storms are likely to differ and depend upon the various parameters including IMF Miyoshi et al, 2007 andShen et al, 2017). Very recently, Turner et al (2019) investigated a detailed statistical study of electron radiation belt response to the geomagnetic storms as a function of energy and L-shell for 30 keV to 6.3 MeV by considering the storms driven by CME shocks/sheaths and ejecta and found depletion of >1 MeV for outer belt and an enhancement of megaelectron volt electrons at lower L-shells. Very recently, Turner et al (2019) investigated a detailed statistical study of electron radiation belt response to the geomagnetic storms as a function of energy and L-shell for 30 keV to 6.3 MeV by considering the storms driven by CME shocks/sheaths and ejecta and found depletion of >1 MeV for outer belt and an enhancement of megaelectron volt electrons at lower L-shells.…”

“…Very recently, Turner et al (2019) investigated a detailed statistical study of electron radiation belt response to the geomagnetic storms as a function of energy and L-shell for 30 keV to 6.3 MeV by considering the storms driven by CME shocks/sheaths and ejecta and found depletion of >1 MeV for outer belt and an enhancement of megaelectron volt electrons at lower L-shells. So more interesting future studies can be carried out by selecting different solar drivers and solar wind parameters for each L-shell indicating inner and outer belt variations as mentioned by Turner et al (2019). So more interesting future studies can be carried out by selecting different solar drivers and solar wind parameters for each L-shell indicating inner and outer belt variations as mentioned by Turner et al (2019).…”

Understanding Electron Dropout Echoes Induced by Interplanetary Shocks: Test Particle Simulations

“…These violent solar phenomena can drive magnetic storms, during which electron radiation belt can vary drastically (e.g., Ganushkina et al, 2015;Katsavrias et al, 2019;Mourenas et al, 2019;Turner et al, 2019, and references therein). The impingement of an IP shock can suddenly compress the magnetosphere, further leading to acceleration and transport of energetic electrons.…”