What Local Sub-auroral Ionospheric Electron Temperature Enhancements Tell Us 
about MI Coupling

C. Gurgiolo, B. Sandel, X.X. Zhang, J. Perez, P. Brandt, and J-M. Jahn 


Local enhancements in the sub-auroral ambient ionospheric electron temperature
are common during disturbed times. Current thinking has it that these result
from a downward directed heat flux generated either by instabilities active in
the region where the ring current overlaps the plasmasphere or by Coulomb
scattering of the plasmaspheric electrons off the heavier ring current ions.  In
this talk we look at sub-auroral ionospheric heating events in the context of
the plasmasphere and ring current to see what they can tell us about MI
coupling.  Data from the IMAGE satellite provides global plasmasphere and ring
current maps and data from the DMSP satellite provides in-situ ionospheric
conditions in the study.  We find that heating events separate into three
categories which we call inner, conjugate outer and non-conjugate outer events. 
Inner events occur well inside the plasmasphere boundary layer and are mostly
observed in the dawn/noon sectors; conjugate outer events occur within the
plasmasphere boundary layer, primarily in the dusk/midnight sectors and mainly
in the substorm growth and early recovery phases; and non-conjugate outer events
are broad regions of heating, often extending beyond the plasmapause and are
observed primarily in the dusk/midnight sectors late in the recovery phase. The
mechanism providing the heat flux in each category does not appear to be the
same, in fact, only with conjugate outer events does it appear that the
conventional models play a role.  With inner events the equatorial hot to cold
density ratio is to small to sustain EMIC waves.  With non-conjugate outer
events the non-conjugacy argues against an equatorial source and the extension
beyond the plasmapause decouples the plasmasphere from the ring-current.  One
possibility which will be explored in the case of non-conjugate outer events is
that the heating is related to processes active in the refilling of the
plasmaspheric flux-tubes.

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