Direct observation of enhanced magnetospheric convection using medium 
energy (1.0-3.0 keV) energetic neutral atoms

J.-M. Jahn, C. Pollock, R. Skoug, M. G. Henderson, M.-C. Fok, and 
G.D. Reeves


Observations of electric field induced magnetospheric convection to a large
extent have relied on the measurements in the low-altitude ionosphere, at 
the foot-points of magnetospheric field lines. Relating those ionospheric
measurements back to the magnetosphere is of course subject to all the know
problems with mapping along magnetic field lines. Another candidate to
measuring magnetospheric convection at least during times of enhanced
convection electric fields are medium energy (1.0 - 3.0 keV) ions traced by
their energetic neutral atom (ENA) signature observed by the MENA 
instrument onboard IMAGE. In this energy range, and under the absence of 
any enhanced electric fields, those ions drift very slowly through the 
inner magnetosphere, requiring tens of hours to pass from geosynchronous 
orbit on the nightside to geosynchronous orbit on the dayside. During a 
single IMAGE orbit (13 hours orbital period) these particles will appear 
stationary when observed by the MENA instrument. However, in cases of 
enhanced convection, these ion populations and their associated ENA 
emissions will visibly move on timescales of an hour, providing a direct 
measurement of the convection electric field. We present observations of 
such events, measuring the drift of medium energy ENA populations through 
the inner magnetosphere and estimating the electric fields responsible for 
those drifts. At this point these measurmenets remain somewhat crude due 
to remaining uncertainties in the exact source location of the observed 
ENA's. Eventually, however, we will compare these measurements to 
measurements taken in the ionosphere below.

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Fall 2002 Meeting of the American Geophysical Union
San Francisco, CA, USA, 6-10 December 2002