Electric Fields From Ion Distributions Extracted from ENA/HENA Images

J. D. Perez (Auburn University, Auburn, AL, 36849), X. X. Zhang, D. G. Mitchell 


Equatorial ion distributions integrated over pitch angle and extracted from
ENA/HENA images are used to determine E-fields in the EarthÕs inner
magnetosphere. The motion of the peaks in the ion distributions are used to
measure drift velocities from which magnetic drift contributions are subtracted
leaving the contribution from the ExB drift. Tsygankeno magnetic fields are
used. Three different storm periods are examined. The first, 11-13 UT, June 10,
2000, shows ions of average energy 33 keV drifting westward from dusk and
eventually disappearing when they reach noon. The E-fields deduced during the
period of drift are in reasonable agreement with the Weimer model. The second,
10-14 UT, August 12, 2000, shows ions injected between midnight and dawn and
then remaining there just after the end of the main phase of a strong storm. The
E-fields necessary to counteract the westward drift due to magnetic curvature
and gradients are stronger than those obtained from the Weimer model. The third,
7-10 UT, October 4, 2000, is during the main phase of the storm and shows
episodic injections between midnight and dawn. Some westward drift is observed
but only for a short distance. There is either rapid decay of these injected
ring current ions or their kinetic energy is increased out of the range of the
HENA instrument as they fall through the electric potential.

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Presented at the August 2003 AGU Chapman Conference, Helsinki, Finland