Unusual Density Structures in the Outer Plasmasphere Near the Magnetic Equator

Dennis L. Gallagher, James L. Green, Bodo W. Reinisch, Xueqin Huang, 
Zine B. Smith 


The magnetic equator has long been known as a region of interaction between
plasma populations, particularly through plasma waves. Here microphysical
processes may participate in the isotropization of field-aligned outflowing
ionospheric plasma that repopulates magnetic field lines evacuated by the
storm-time enhanced convection electric field. Olsen et al. [1987] reported
direct evidence for trapped H+ ions at the magnetic equator in the presence of
ion cyclotron and/or lower hybrid waves. They further reported no corresponding
variation in total density, except for an occasional dip in density at the
magnetic equator. IMAGE radio plasma imager (RPI) and extreme ultraviolet imager
(EUV) measurements, of H+ and He+ respectively, appear to suggest the presence
of enhanced equatorial plasma density in the outer plasmasphere during storm
recovery times. Some field refilling models postulate the transient existence of
field-aligned density structures, which have not so far been observed. We will
present the results of RPI and EUV analysis of these observed outer
plasmaspheric features and discuss the implications in light of past
observations and theory.

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Fall Meeting, American Geophysical Union, San Francisco, U.S.A., 2005