Global Response of the Outer Radiation Belt to Geomagnetic Activity: Transport 
and Losses

A.Y. Ukhorskiy, B.J. Anderson, K. Takahashi, P. Brandt, and N.A. Tsyganenko
 

During geomagnetic storms relativistic electrons in EarthÕs outer radiation belt
exhibit highly nonlinear behavior. Electron fluxes in the belt vary over several
orders in magnitude on the time scales from minutes to days. This work addresses
radial transport and losses of radiation belt electrons during storms. For this
purpose we developed a new semi-empirical model of the belt.  The model is based
on a test particle simulations of energetic electron motion in storm-time
electric and magnetic fields. Global variations of magnetospheric electric and
magnetic fields are derived from a dynamic model of geomagnetic field, for which
the inductive electric field is calculated in a self-consistent fashion.  We
show that impulsive changes in solar wind dynamic pressure can result in rapid
electron scattering across the drift shells, which identifies the dynamic
pressure as one of the primary mechanisms of radial transport in the belt. Our
calculations show that electron motion is inconsistent with radial diffusion,
and hence a more detailed description is required for accurate predictions of
electron fluxes in the belt. It is also shown that ring current enhancement
during storm main phase can produce a substantial impact on electron motion. In
particular, during large storms diamagnetic effect due to partial ring current
sufficiently changes magnetic field structure in the inner magnetosphere leading
to rapid magnetopause losses of radiation belt electrons.

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Global Aspects of Magnetosphere-Ionosphere Coupling, 2006 Yosemite Workshop, 
Yosemite National Park, CA, USA, 7-10 February 2006