Contribution of Enhanced Radial Transport to the Acceleration of Radiation Belt Electrons

Details Contribution of Enhanced Radial Transport to the Acceleration of Radiation Belt Electrons Contribution of Enhanced Radial Transport to the Acceleration of Radiation Belt Electrons

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm41d..02h&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SM41D-02

Physics

2720 Energetic Particles: Trapped

Scientific paper

Radial transport accelerates radiation belt electrons conserving their first adiabatic invariant, increasing perpendicular relative to parallel energy and producing pitch angle distributions which should be measurably anisotropic in the absence of wave processes causing pitch angle scattering. Enhanced convection and substorm injection during intervals driven by high solar wind speed and southward IMF Bz produce a seed population of superthermal electrons which can be transported radially inward by fluctuations in the convection electric field. However, additional processes greatly enhance the radial transport rate on time scales as fast as an electron drift period. The most dramatic is acceleration by the induction electric field produced by a strong interplanetary shock associated with a high speed CME impinging on the magnetosphere. The March 24, 1991 production of new > 10 MeV electron and proton radiation belts at L=2.5 is the prime and best studied example of this mechanism which occurs rarely for electrons and more frequently for protons due to the existence of a Solar Energetic Proton source population into L=4 at shock arrival drift resonant with the magnetosonic impulse launched inside the magnetosphere. In the absence of a strong shock or electron seed population sufficiently hard for drift resonance, the more common mechanism for electron radial transport is diffusive over many drift period. Radial diffusion is enhanced by the excitation of ULF oscillations with periods comparable to the electron drift time and violating the third adiabatic invariant. ULF wave enhancement is well correlated with electron acceleration at L > 4.5 during the recovery phase of geomagnetic storms1. The dynamics of relativistic electrons in ULF wave fields has been simulated using guiding center approximation equations to track the drift (and bounce) motion of particles. The effects of ULF wave frequency and L-dependence are included self-consistently with a field prescription from MHD simulations of solar wind interaction with the magnetosphere using the Lyon-Fedder-Mobary (LFM) 3D MHD code. Examples using specific solar wind drivers like an interplanetary shock, high speed solar wind and solar wind pressure oscillations will be discussed. 1 O'Brien, T. P. et al., J. Geophys. Res., 108(A8), 1329, doi:10.1029/2002JA009784, 2003.

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