Acceleration of radiation belt electrons and the role of the average interplanetary magnetic field B_z component in high‐speed streams

Abstract

In this study we examine the recovery of relativistic radiation belt electrons on 15–16 November 2014, after a previous reduction in the electron flux resulting from the passage of a corotating interaction region (CIR). Following the CIR, there was a period of high‐speed streams characterized by large, nonlinear fluctuations in the interplanetary magnetic field (IMF) components. However, the outer radiation belt electron flux remained at a low level for several days before it increased in two major steps. The first increase is associated with the IMF background field turning from slightly northward on average to slightly southward on average. The second major increase is associated with an increase in the solar wind velocity during a period of southward average IMF background field. We present evidence that when the IMF Bz is negative on average, the whistler mode chorus wave power is enhanced in the outer radiation belt, and the amplification of magnetic integrated power spectral density in the ULF frequency range, in the nightside magnetosphere, is more efficient as compared to cases in which the mean IMF Bz is positive. Preliminary analysis of the time evolution of phase space density radial profiles did not provide conclusive evidence on which electron acceleration mechanism is the dominant. We argue that the acceleration of radiation belt electrons requires (i) a seed population of keV electrons injected into the inner magnetosphere by substorms and both (ii) enhanced whistler mode chorus waves activity as well as (iii) large‐amplitude MHD waves.

High‐Energy Electron Flux Enhancement Pattern in the Outer Radiation Belt in Response to the Alfvénic Fluctuations Within High‐Speed Solar Wind Stream: A Statistical Analysis

“…The interplanetary medium parameters measured at the L1 Lagrangian point are analyzed for each selected event, in which the kind of solar wind structure is identified. Curiously, the high-energy electron flux enhancement pattern observed here in the 37 events is similar to some of the case studies published in the literature (see Da Silva et al, 2019;Jaynes et al, 2015;Souza et al, 2017), that are coincident with the occurrences of HSSs, specifically during the Alfvénic fluctuations period. Thereby, the methodology applied here will be consistent with the approaches discussed by those authors.…”

Contribution of ULF Wave Activity to the Global Recovery of the Outer Radiation Belt During the Passage of a High‐Speed Solar Wind Stream Observed in September 2014

“…PhSD data for Radiation Belt Storm Probes (RBSP)‐A were obtained directly from https://www.rbsp-ect.lanl.gov/data_pub/PSD/. We use values of μ = 2291 MeV/G and K = 0.1145 G 1∕2 R E because they optimize the coverage of L * while limiting the equatorial PhSD to approximately 45–90° pitch angle range (see Reeves et al, ; Souza et al, ). It is important to highlight that the higher μ value chosen corresponds to electrons at energies ≳1.5 MeV, at which the increase in the outer belt flux is observed.…”

Dynamic Mechanisms Associated With High‐Energy Electron Flux Dropout in the Earth's Outer Radiation Belt Under the Influence of a Coronal Mass Ejection Sheath Region

“…It also has been widely used to address the low-frequency waves generation (in a few to tens of mHz range) like the ULF waves in the inner magnetosphere, specifically in the radiation belts (e.g., Alves et al, 2016;Claudepierre et al, 2010Claudepierre et al, , 2008Da Silva et al, 2019;Jauer et al, 2019;Komar et al, 2017;Souza et al, 2017). Da Silva et al (2019) and Souza et al (2017) used the SWMF/BATS-R-US model to study the ULF waves in the equatorial and nightside magnetosphere during the influence of the Alfvénic fluctuations associated with HSS. Claudepierre et al (2008) used the Lyon-Fedder-Mobarry (LFM) model to study the production of ULF waves in the magnetosphere to the HSS.…”

“…It is extensively used by the scientific community to study the large-scale interaction between different solar wind structures and Earth's magnetosphere. It also has been widely used to address the low-frequency waves generation (in a few to tens of mHz range) like the ULF waves in the inner magnetosphere, specifically in the radiation belts (e.g., Alves et al, 2016;Claudepierre et al, 2010Claudepierre et al, , 2008Da Silva et al, 2019;Jauer et al, 2019;Komar et al, 2017;Souza et al, 2017). Da Silva et al (2019) and Souza et al (2017) model to study the production of ULF waves in the magnetosphere to the HSS.…”

“…(2019) and Souza et al. (2017) used the SWMF/BATS‐R‐US model to study the ULF waves in the equatorial and nightside magnetosphere during the influence of the Alfvénic fluctuations associated with HSS. Claudepierre et al.…”