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Ann. Geophys., 24, 3151-3159, 2006
www.ann-geophys.net/24/3151/2006/
© European Geosciences Union 2006
Relativistic electron dropouts by pitch angle scattering in the geomagnetic tail
J. J. Lee1, G. K. Parks1, K. W. Min2, M. P. McCarthy3, E. S. Lee1, H. J. Kim2, J. H. Park2, and J. A. Hwang2
1Space Sciences Lab., University of California, Berkeley, CA, USA
2Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, Korea
3Geophysics Program, University of Washington, Seattle, USA
Abstract. Relativistic electron dropout (RED) events are characterized by fast electron
flux decrease at the geostationary orbit. It is known that the main loss
process is non adiabatic and more effective for the high energy particles.
RED events generally start to occur at midnight sector and propagate to noon
sector and are correlated with magnetic field stretching. In this paper, we
discuss this kind of event can be caused from pitch angle diffusion induced
when the gyro radius of the electrons is comparable to the radius of
curvature of the magnetic field and the magnetic moment is not conserved any
more. While this process has been studied theoretically, the question is
whether electron precipitation could be explained with this process for the
real field configuration. This paper will show that this process can
successfully explain the precipitation that occurred on 14 June 2004
observed by the low-altitude (680 km) polar orbiting Korean satellite,
STSAT-1. In this precipitation event, the energy dispersion showed higher
energy electron precipitation occurred at lower L values. This feature is a
good indicator that precipitation was caused by the magnetic moment
scattering in the geomagnetic tail. This interpretation is supported by the
geosynchronous satellite GOES observations that showed significant magnetic
field distortion occurred on the night side accompanying the electron flux
depletion. Tsyganenko-01 model also shows the magnetic moment scattering
could occur under the geomagnetic conditions existing at that time. We
suggest the pitch angle scattering by field curvature violating the first
adiabatic invariant as a possible candidate for loss mechanism of
relativistic electrons in radiation belt.
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