Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm42c02a&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SM42C-02
Physics
2708 Current Systems (2409), 2740 Magnetospheric Configuration And Dynamics, 2788 Storms And Substorms
Scientific paper
Our understanding of magnetosphere-ionosphere coupling during geomagnetic storms is severely hampered by the observational challenge that storms present: the ionospheric manifestations of the coupling typically expand equatorward of our extensive ground observation systems, e.g. magnetometers and radars. The Iridium system, more than 70 satellites in circular, polar, 780 km altitude orbits in six equally spaced planes, provides an ideal system for monitoring the global distribution of field aligned currents because each of the Iridium satellites carries an engineering magnetometer which has sufficient resolution to sense the Birkeland currents. Moreover, the Iridium system provides complete coverage of the currents throughout geomagnetic storms regardless how far equatorward the auroral oval expands. Techniques to determine the global field aligned current (FAC) distribution have been developed that use only the magnetic field measurements from the Iridium satellites and make no assumptions regarding ionospheric conductivity or global magnetic activity parameters (e.g., AE, Kp or Dst) and are therefore totally independent of indices which might be suspect during storm time. The primary limitation of the Iridium data is that the sampling rates are low so that we require one-hour accumulation times to derive reliable FAC patterns. Nonetheless, the data provides the first ever continuous monitoring of the global FACs through geomagnetic storms. Data for scientific study has been acquired beginning in mid February 1999 and since that time there have been over twenty geomagnetic storms for which Iridium and correlative ACE solar wind data are available. For the time scales we can resolve, we find that the IMF is the primary determining factor in both the intensity and latitude of FACs. The FACs are enhanced during storm main phase but recover rapidly, often within an hour, at the end of the main phase depending somewhat on how strongly the IMF turns northward. The size of the auroral oval however takes longer to retreat to pre-storm latitudes, about six hours. The FAC distributions therefore recover to pre-storm configurations very early in storm recovery as indicated by Dst. The data are also used to assess whether or not the total FAC displays saturation effects.
Anderson Benjamin J.
Ohtani Shin
Waters Colin L.
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