Relativistic electron acceleration during HILDCAA events: are precursor CIR magnetic storms important?

Abstract

We present a comparative study of high-intensity long-duration continuous AE activity (HILDCAA) events, both isolated and those occurring in the "recovery phase" of geomagnetic storms induced by corotating interaction regions (CIRs). The aim of this study is to determine the difference, if any, in relativistic electron acceleration and magnetospheric energy deposition. All HILDCAA events in solar cycle 23 (from 1995 through 2008) are used in this study. Isolated HILDCAA events are characterized by enhanced fluxes of relativistic electrons compared to the pre-event flux levels. CIR magnetic storms followed by HILDCAA events show almost the same relativistic electron signatures. Cluster 1 spacecraft showed the presence of intense whistler-mode chorus waves in the outer magnetosphere during all HILDCAA intervals (when Cluster data were available). The storm-related HILDCAA events are characterized by slightly lower solar wind input energy and larger magnetospheric/ionospheric dissipation energy compared with the isolated events. A quantitative assessment shows that the mean ring current dissipation is~34 % higher for the storm-related events relative to the isolated events, whereas Joule heating and auroral precipitation display no (statistically) distinguishable differences. On the average, the isolated events are found to be comparatively weaker and shorter than the storm-related events, although the geomagnetic characteristics of both classes of events bear no statistically significant difference. It is concluded that the CIR storms preceding the HILDCAAs have little to do with the acceleration of relativistic electrons. Our hypothesis is that~10-100-keV electrons are sporadically injected into the magnetosphere during HILDCAA events, the anisotropic electrons continuously generate electromagnetic chorus plasma waves, and the chorus then continuously accelerates the high-energy portion of this electron spectrum to MeV energies.

A Review of Alfvénic Turbulence in High‐Speed Solar Wind Streams: Hints From Cometary Plasma Turbulence

“…The chorus in turn accelerates the ~100 keV electrons to relativistic energies. Reviews of this idea can be found in Tsurutani et al (, ), Kasahara et al (), Miyoshi et al (), and Hajra, Tsurutani, Echer, Gonzalez, Santolik (), Hajra, Tsurutani, Echer, Gonzalez, Brum, et al ().…”

Cross-correlation and cross-wavelet analyses of the solar wind IMF Bz and auroral electrojet index AE coupling during HILDCAAs

“…Due to the injection of ∼ 10-100 keV electrons during the HILDCAAs, these events can lead to the acceleration of relativistic (∼ MeV) electrons in the outer Van Allen radiation belt (Hajra et al, 2014b(Hajra et al, , 2015aTsurutani et al, 2016). The relativistic "killer" electrons can cause rapid degradation of semiconductors and satellite sensors in orbits in this region (Guarnieri, 2005;Hajra et al, 2014bHajra et al, , 2015a.…”

“…The relativistic "killer" electrons can cause rapid degradation of semiconductors and satellite sensors in orbits in this region (Guarnieri, 2005;Hajra et al, 2014bHajra et al, , 2015a.…”

Evidence of prompt penetration electric fields during HILDCAA events

“…In addition to that mentioned above, HILDCAA is associated with the enhancement of magnetospheric relativistic electrons. Hajra et al (2015) compared it to the isolated HILDCAA events. They assume that about 10-100 keV electrons are injected into the inner magnetosphere during the events, so the anisotropic electrons generate electromagnetic chorus plasma waves constantly, and the chorus waves continuously accelerate the electron to MeV energies (Paulikas and Blake, 1979;Baker et al, 1986;Summers et al, 1998;Meredith et al, 2003;Tsurutani et al, 2006bTsurutani et al, , 2010.…”