Evolution of seed electrons and chorus waves during high speed stream driven storms observed on THEMIS

Details Evolution of seed electrons and chorus waves during high speed stream driven storms observed on THEMIS Evolution of seed electrons and chorus waves during high speed stream driven storms observed on THEMIS

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm13b2041l&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM13B-2041

Physics

Plasma Physics

[2774] Magnetospheric Physics / Radiation Belts, [2778] Magnetospheric Physics / Ring Current, [6984] Radio Science / Waves In Plasma, [7867] Space Plasma Physics / Wave/Particle Interactions

Scientific paper

During high speed stream (HSS) driven storms, relativistic electron fluxes in the outer radiation belt decrease during the main phase, followed by an 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 seed electrons and chorus waves in the context of various storm phases is not well understood. In this study we use observations from THEMIS over the period of 2008-2011 to perform a superposed epoch analysis of the evolution of seed electrons and chorus waves during various phases of HSS driven storms. Our results provide insight into their role in relativistic electron flux evolution. The phase space density of seed electrons with a first adiabatic invariant μ in the range 1-30 MeV/G, increases during the main phase followed by a slow decay during the recovery phase. Importantly, the evolution of the seed electron population is highly dependent on stream geoefficiency and it also varies at different μ and MLT. A stream is geoeffective if the imbedded IMF obeys the Russell-McPherron rule "Spring To Fall Away". Wave amplitude and occurrence rate of chorus waves increase substantially after the storm onset during the main phase and are elevated for a few days in the following recovery phase of the storm. Clear dependence of chorus wave activity is found on stream geoefficiency and MLT. We suggest that the increases of both seed electron phase space density and chorus activity during HSS after the storm onset contribute to the increase in relativistic electron fluxes in the recovery phase of HSS driven storms, but other mechanisms are needed to explain the relativistic electron flux dropout during the storm main phase. In addition, we also briefly discuss the evolution of seed electron population and chorus waves during the period 2008-2011 that includes part of the unusually quiet and extended minimum between solar cycles 23 and 24, and the rising phase of cycle 24.

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