Energetic electron (>10 keV) microburst precipitation, ~5–15 s X-ray pulsations, chorus, and wave-particle interactions: A review

Abstract

The fundamental features of ~0.1–0.2 s duration ~0.5 s spaced ionospheric electron precipitation “microbursts,” ~5 to 15 s microburst “trains,” and 5–15 s electron precipitation pulsations are reviewed in light of similar temporal structures of electromagnetic whistler mode “chorus” waves detected in the outer magnetosphere. Past observations of microbursts point to extremely rapid (ms timescale) wave-particle interactions, probably between lower band chorus subelements (durations of ~10 to 100 ms) and energetic ~10 to 100 keV electrons. A recent theory explaining such rapid interaction rates observed in microbursts is briefly reviewed. Arguments are given why ~5–15 s X-ray (and optical) pulsations are also associated with chorus scattering of energetic electrons. Comments about relativistic (E > 1 MeV) microbursts are also provided. There are, however, many other unsolved problems of outer zone energetic electron precipitation. The authors will attempt to indicate several of these for the interested reader. Finally, an appendix is provided for a brief review of two-frequency chorus and some current problems with that topic.