Overlap of the Plasmasphere and Ring Current: Relation to Subauroral Ionospheric 
Heating 

C. Gurgiolo, B.R. Sandel, J.D. Perez, D.G. Mitchell, C.J. Pollock, 
and B.A. Larsen  


The overlap of the ring-current with the outer plasmasphere is thought to play a
major role in storm-time related increases in the sub-auroral ambient topside
electron temperature. Instabilities generated within the overlap region, Coulomb
collisions of plasmaspheric electrons with the ring-current ions, and charge
exchange are all thought to work either individually or together to generate a
downward heat flux into the ionosphere to produce the increase in temperature.
Analysis of IMAGE 2D ring current and plasmasphere density maps together with
in-situ DMSP ambient electron temperature data shows that the heating generally
occurs over a small radial extent within the plasmasphere / ring current overlap
region and may be significantly earthward of the plasmapause. This argues
against collisional heat conduction as the source of the heat flux and for an
instability based process. The finding that the heating 7occurs within well
defined ratios of the cold plasmasphere to hot ring current density strengthens
this supposition. 

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Journal of Geophysical Research, in press, 2005