Paper#: 145
Poster #:
Session Name: Workshop 6B: Inonspheric Process
Room: 200ABC
Day: Thursday
Time: 3:45-4:10 p.m.
Abstract Title: The Storm - Substorm Relationship: Are Substorms Responsible for Ionospheric-Source Ions in the Ring Current?
PresentSurname: Mitchell, D.G.
All Authors: D.G. Mitchell, P.C. son Brandt, E.C. Roelof, D.C. Hamilton, K.C. Retterer, T.E. Moore
Abstract : The High Energy Neutral Atom imager (HENA) on the NASA IMAGE MidEx mission has provided nearly continuous imaging of the energetic neutral atom emission from the near-Earth magnetosphere for almost two years. Within the past six months, an additional capability for independently accumulating images of 15 - 120 keV hydrogen and 80 - 250 keV oxygen emission has been achieved. The oxygen images provide the means for separately following the dynamics and relative abundance of protons and oxygen during magnetic storms and substorms. Because this technique relies on the charge exchange between singly charged ions and the ambient neutral gas population, the ENA emission cannot be detected beyond approximately 12 Re for strong events, and is limited to perhaps 6 Re for weak events. This makes the investigation of magnetotail substorm dynamics more difficult, and biases the analysis toward larger, usually storm-associated substorms. Nevertheless, some interesting results are emerging, with the suggestion that substorms play a central role in the composition of the ring current during magnetic storms. In particular, the appearance of high fractions of oxygen ENA in the 100 to 250 keV energy range is strongly correlated with substorm activity. Whether that correlation depends on sources (i.e., extraction of oxygen from the ionosphere and acceleration to ring current energies) or losses (enhanced ENA flux resulting from the pitch-angle scattering of already entrained O+, with subsequent strong ENA emission from the interaction with the exobase) is not yet clear. We will discuss the ongoing analysis of these observations.