Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm42a..04k&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SM42A-04
Physics
2409 Current Systems (2708), 2431 Ionosphere/Magnetosphere Interactions (2736), 2437 Ionospheric Dynamics, 2447 Modeling And Forecasting, 2475 Polar Cap Ionosphere
Scientific paper
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 {y} component. After a sign reversal of B {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 {y} component. Following a brief interval of positive B {y}, the B {y} component turns negative once again, and the IMF transitions beyond its initial northward direction toward positive B {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 60o for northward IMF to 40o 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.
Anderson Benjamin J.
Korth Haje
Lyon John G.
Wiltberger Michael J.
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