Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm31a0301b&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM31A-0301
Physics
2721 Field-Aligned Currents And Current Systems (2409), 2776 Polar Cap Phenomena, 2784 Solar Wind/Magnetosphere Interactions, 2788 Magnetic Storms And Substorms (7954)
Scientific paper
Magnetic field data from the constellation of more than 70 Iridium satellites has been collected for science analysis since February 1999. Key parameters derived from these data providing the current intensity and co- latitude of the currents and evaluations of the total Birkeland current are used with ACE solar wind and IMF observations to assess the dynamics of Birkeland currents during storms. A total of 99 storms with minimum Dst of -80 nT or less were analyzed from February 1999 through December 2005. To assess the time development we consider three types of storms: (1) storms with sharp onsets, evidenced by sharp southward turnings of the IMF at the start of the storm main phase; (2) storms with a gradual main phase onset corresponding to a gradual southward IMF turning; and (3) storms with sharp transitions to the recovery phase. After accounting for the accumulation time in the Iridium processing and delay from ACE to Earth we find that there is approximately a 40 minute delay between maximum duskward solar wind electric field, Ey, for sharp onset storms. The currents remain intensified and expanded to lower latitudes up to three hours after the forcing decreases. The maximum current intensity is delayed by about 1 hour and the total field aligned current by almost 2 hours after maximum Ey and their decay after Ey decreases is delayed by at least 3 hours. For sharp turn off storms the poleward retreat and current intensity exhibit an initial prompt response followed by a slow, several hour decay. Both the equatorward expansion and peak total current saturate for Ey > 10 mV/m. The results imply that internal dynamics of the magnetosphere act to regulate the system response to solar wind driving. In particular, the dependence of equatorward expansion on Ey means that the lobes grow for strong forcing, implying that the magnetotail structure changes to facilitate greater tail reconnection to balance the enhanced driven convection.
Anderson Benjamin J.
Bodurtha K. E.
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