Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm22a0574j&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM22A-0574
Other
2712 Electric Fields (2411), 2716 Energetic Particles, Precipitating, 2720 Energetic Particles, Trapped, 2730 Magnetosphere: Inner, 2760 Plasma Convection
Scientific paper
Observations of electric field induced magnetospheric convection to a large extent have relied on 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 measure 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. This technique allows us to observe the global transport of actual magnetospheric material, rather than inferring that motion from the mapping of low-altitude measurements. We compare our measurements to simulation results of the presented time periods. At this point the ENA measurements 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.
Fok M. H.
Henderson Gideon M.
Jahn J.-
Pollock C. J.
Reeves Galen
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