Simultaneous observation of magnetospheric neutral atoms and proton aurora

S. B., Mende1, H. U. Frey1, T. J. Immel1
  Space Sciences Laboratory, University of California, Berkeley, CA 94720
D. G. Mitchell2, C:son-Brandt2, 
  The Johns Hopkins University, Laurel, MD  20723
J.-C. Gerard3, 
  University of Liege, Liege, Belgium

Data from the High Energy Neutral Atom (ENA) and the far ultraviolet
(FUV) imagers on IMAGE were compared for a six hour period during which
a reasonably intense substorm occurred.  The substorm presented is
typical of a substorm expansive phase showing that while the total
electron precipitation suddenly increase one whole order of magnitude,
the protons increase only about 50%.  In principle ENA images represent
the trapped fluxes in the magnetosphere while the proton aurora measured
by the FUV SI12 instrument represents the precipitating component.  At
substorm onset the increase in intensity of the auroral protons and
electrons is very sudden while the intensification of the ENA-s coming
from regions of L<6 is much more gradual. The intensification of the
precipitating electrons is relatively short lived (~ 10 minutes) while
the ENA enhancements are long lived (almost a whole hour).  Just prior
to the substorm expansive phase (in the growth phase) the precipitated
proton and electron fluxes encounter a minimum while the ENA-s show a
slight growth.