Evolution of chorus waves and their source electrons during storms driven by corotating interaction regions

Abstract

[1] During Corotating Interaction Region (CIR)-driven storms, relativistic electron fluxes in the outer radiation belt decrease in the main phase, followed by a gradual increase in the recovery phase. Recent studies have shown that whistler mode chorus waves play an important role in accelerating the seed electron population to relativistic energies in the outer radiation belt. However, the evolution of chorus waves and their source electrons responsible for the wave excitation during storm various phases is not well understood. In this study we select 72 CIR-driven storm periods over the interval 2007-2011 to perform superposed epoch analysis of the evolution of chorus waves and source electrons in the L* and MLT range extensively observed by THEMIS during various phases of CIR-driven storms. The wave amplitudes and the occurrence of chorus waves substantially increase and peak in the main phase and gradually decrease in the following recovery phase at L* < $7. The phase space density of source electrons at L* < $7 also increases in the main phase followed by a gradual decay in the recovery phase, showing a remarkable consistency with the evolution of chorus waves. Importantly, the evolution of the chorus wave activity and source electron population is highly dependent on the preceding interplanetary magnetic field (IMF) B z orientation. Our results suggest that the increased activity of chorus waves and source electrons may contribute to the enhanced radiation belt electron flux in the recovery phase of CIR-driven storms, but an additional mechanism is probably required to explain the main phase dropout.

The Storm Time Development of Source Electrons and Chorus Wave Activity During CME‐ and CIR‐Driven Storms

“…The CIR storms in this study do not show a larger recovery phase Kp, so it is not surprising that while the results here agree with those of Spasojevic (2014) during the main phase, they do not show the same recovery phase feature. The results of this study show that the measured chorus wave activity and the source electron population along with the corresponding chorus wave growth proxy are most enhanced during the main phase in the inner magnetosphere between L = 3-6, matching the results from Li et al (2012) and Spasojevic (2014), and that while the results here do not directly match those by MacDonald et al (2008MacDonald et al ( , 2010, the discrepancies can be explained by field line stretching outside of the chorus source region observed at geosynchronous orbit. Journal of Geophysical Research: Space Physics observations at South Pole Station showed a strong dropout in chorus activity and amplitude during the main phase.…”

“…Spasojevic (2014) showed using Antarctic magnetometer data from 2000 to 2010 that CME-and CIR-driven storms had very little difference in chorus occurrence and amplitude with an exception of the half day after minimum Dst*, in which CIR storms had higher occurrence rates and higher average Kp. Li et al (2012) showed using THEMIS observations between L* = 5-9 that 10 MeV/G of source electrons were most enhanced around minimum Dst between L* = 5-9, while chorus activity was strongest then as well. Spasojevic (2014) also showed a storm intensity dependence on chorus amplitude and occurrence, as larger storms had more, stronger, and longer lasting chorus activity than moderate storms.…”

“…The inner edge of the storm time enhancement of tens of keV electrons has been found to be ordered with a ΔL outward from the plasmapause of~1 (Khoo et al, 2018). Li et al (2012) and Miyoshi et al (2013Miyoshi et al ( , 2016 compared the evolution of chorus wave power and source electrons (from a few to tens of keV) during CIRs with predominately northward and southward oriented interplanetary magnetic field Bz, showing that the solar wind differences drove changes in the source electrons and levels of chorus wave activity. Subsequently, Katus et al (2015) found that average plasmapause location was lower in L-shell across the dayside during the main phase of CME-driven storms compared to CIR-driven storms.…”

Space Weather Effects Produced by the Ring Current Particles

“…This anisotropic population of ring current energy electrons is often called the "seed" population, wherein the source of the free energy for chorus wave growth is available. Chorus waves interact with "seed" electrons at energies of 10's to 100's of keV through cyclotron resonance and can accelerate electrons to very high energies (Kennel and Petschek 1966;Kennel and Thorne 1967;Li et al 2008Li et al , 2012Thorne 2010). Whistler-mode chorus plays a critical role in accelerating ring current electrons to relativistic energies in the outer belt (Horne et al 2005;Green 2006;Chen et al 2007), including to "killer" electron energies that can have disastrous space weather consequences to sensitive systems (Baker 2001;Fennell et al 2001).…”

High‐speed solar wind with southward interplanetary magnetic field causes relativistic electron flux enhancement of the outer radiation belt via enhanced condition of whistler waves

“…Lyons et al [2005] indicated that the enhancement of both relativistic electrons and the whistler mode waves that drive the electron acceleration processes are associated with the enhanced convection driven by Alfvenic fluctuations within an HSS. More recently, Li et al [2012] showed a superposed epoch analysis of chorus waves and hot electrons about CIR-driven storms using Time History of Events and Macroscale Interactions during Substorms data. The evolutions of chorus wave activity and source electron population depend greatly on the preceding IMF-Bz orientation.…”