HR: 11:05h
AN: SM42A-04    [Abstracts]
TI: Comparison of Iridium Observations of Birkeland Currents Associated With Two Magnetic Cloud Events With MHD Simulations
AU: * Korth, H
EM: haje.korth@jhuapl.edu
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723 United States
AU: Anderson, B J
EM: brian.anderson@jhuapl.edu
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723 United States
AU: Lyon, J G
EM: lyon@tinman.dartmouth.edu
AF: Dartmouth College, 6127 Wilder Lab, Hanover, NH 03755 United States
AU: Wiltberger, M J
EM: wiltbemj@ucar.edu
AF: NCAR/HAO, 3450 Mitchel Lane, Boulder, CO 80301 United States
AB: We present global observations of Birkeland currents associated with two magnetic clouds passing by the Earth's magnetosphere. During the first event on 19--21 March 2001, the interplanetary magnetic field (IMF) is initially oriented southward with a negative $B_\mathrm{y}$ component. After a sign reversal of $B_\mathrm{y}$, the IMF turns increasingly northward over the course of 36 hours. For the second event on 17--19 August 2003, the IMF is initially directed due northward and subsequently turns strongly southward while sustaining a negative IMF $B_\mathrm{y}$ component. Following a brief interval of positive $B_\mathrm{y}$, the $B_\mathrm{y}$ component turns negative once again, and the IMF transitions beyond its initial northward direction toward positive $B_\mathrm{y}$ within a 24-hour period. The events were specifically chosen because of the slow transitions in the IMF orientation and because of the differences in the IMF rotation between the two events. The transitions are slow enough to derive global maps of Birkeland currents from the 70 satellites of the Iridium constellation. The Birkeland current distributions observed by Iridium show characteristic variations in response to changes in IMF orientation, and the most equatorward latitude of the Birkeland currents expands from $60^\circ$ for northward IMF to $40^\circ$ during southward IMF orientation. MHD simulations, driven by solar wind conditions observed during the magnetic cloud events, exhibit variations similar to the ones observed by Iridium. We compare the Iridium Birkeland current distributions obtained during the two events with the MHD simulation results and examine the temporal development of the Birkeland currents between observations and simulations.
DE: 2409 Current systems (2708)
DE: 2431 Ionosphere/magnetosphere interactions (2736)
DE: 2437 Ionospheric dynamics
DE: 2447 Modeling and forecasting
DE: 2475 Polar cap ionosphere
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting