Evolution of pitch angle distributions of relativistic electrons in the radiation belt during magnetic storms

Details Evolution of pitch angle distributions of relativistic electrons in the radiation belt during magnetic storms Evolution of pitch angle distributions of relativistic electrons in the radiation belt during magnetic storms

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm33a0441n&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SM33A-0441

Physics

2720 Energetic Particles: Trapped, 2730 Magnetosphere: Inner, 2774 Radiation Belts

Scientific paper

In order to investigate the storm-time evolution of pitch angle distributions of relativistic electrons in the radiation belt, relativistic electron flux data obtained from the RDM instrument on board the Akebono satellite [Takagi et al., 1993], and MEA instrument on board the CRRES satellite [Vampola et al., 1992] are analyzed within a period of 1989-1998. Pitch angle distributions of these relativistic electrons show a change of the pancake-type distribution into the dumbbell-type distribution during a geomagnetic storm in the slot region and the inner radiation belt especially in the higher energy range. The most strong dumbbell-type distributions are observed during the main and early recovery phase, and these distributions gradually return to the pancake distributions during the following recovery phase. The fast response of the pitch angle distribution associated with the onset of geomagnetic storms can be interpreted by an adiabatic cooling process due to the decrease of the ambient magnetic field intensity associated with the development of the ring current. From the guiding center simulations, it has been clarified that electrons with pancake-type distributions during prestorm periods experience the inverse processes of the betatron and Fermi acceleration, and their equatorial pitch angles become smaller by the Dst effect. The change of pitch angle by this process is consistent with the observation by the CRRES satellite. These facts indicate that, in MeV energy range, adiabatic effects are important especially in the slot region and the inner radiation belt. It is estimated that dynamics of relativistic electrons are governed by the magnetic field at L<2.6, while injections or wave accelerations dominantly proceed at L>2.6.

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