Tuesday, 8 January 2013: 4:15 PM
Room 16B (Austin Convention Center)
Geomagnetic storms are a source of electromagnetic and particle energy deposition that raise the exospheric temperature, change the state of the thermosphere and drive waves of density perturbations from polar regions toward the equator. These traveling atmospheric disturbances cause minute changes in low Earth orbit satellite trajectories that challenge spacecraft operators. Recently the Dst index has been used in operational satellite drag forecasts as a proxy for geomagnetic forcing. Here we report on new insights gained from investigating thermospheric storm responses that significantly departed from the expected Dst-based forecast. These problem storms have a strong association with the sheath regions ahead of interplanetary coronal mass ejections (ICMEs). Rapidly propagating sheath regions produce the initial phase of geomagnetic storms, which in turn, drive significant changes to dayside storm-time energetics compared to the energetics driven by ICMEs with less obvious sheath structure. A superposed epoch analysis reveals distinct behavior of the magnetosphere-ionosphere-thermosphere system during the sheath driven events and suggests that significant energy enters geospace before the main phase Dst storm develops.
In addition to meteorological sensors, the Defense Meteorological Satellite Program (DMSP) spacecraft carry several space environment instruments. We show that magnetic perturbations, Poynting flux, and low energy particle deposition measured during dayside transits of the DMSP spacecraft are enhanced during the poorly forecast events, compared to those events that were well specified by the Dst Index. For cases in which a solar wind transient is accompanied by a leading sheath, these enhancements in high-latitude magnetic perturbations appear hours in advance of the density response. Thus, it is possible, with appropriate processing of the high-latitude polar spacecraft data, to provide important insight and foresight into the subsequent state of the neutral atmosphere beyond that provided by the Dst index.
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