Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm52b01l&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SM52B-01
Physics
2752 Mhd Waves And Instabilities, 2784 Solar Wind/Magnetosphere Interactions, 7851 Shock Waves, 7871 Waves And Instabilities, 7894 Instruments And Techniques
Scientific paper
On May ll, 1999 the solar wind density fell to an unusually low value of ~0.2 cm-3, a period that has come to be known as the day the solar wind almost dissappeared. The Earth's magnetosphere and bowshock moved substantially sunward as a result of the low dynamic pressure and low Mach number (Mms ~ 1.3). The Wind spacecraft observed the bow shock 52 RE upstream of Earth, at the time, the most sunward terrestrial shock crossing ever observed. Under typical solar wind conditions (Mms ~ 10) a parallel shock will energize and reflect ions into the upstream region which subsequently produce waves in the frequency range .01-1 Hz. This shock is too weak to produce these upstream ions, nevertheless broadband righthand polarized waves in the range .01-1 Hz are observed for a 24 hour period upstream of the shock. The wave activity is much lower downstream of the shock. We use Cross-Wavelet analysis of magnetic field and solar wind velocity fluctuations to show that broadband circularly polarized (0.01-1.0 Hz) whistler waves are travelling upstream of the shock, while at the same time lower frequency Alfven waves, presumably of solar wind origin, are travelling in the opposite direction. The whistler waves are able to escape from the shock transition because their group velocity exceeds the solar wind velocity.
Larson Davin E.
Lin Robert P.
Szabo Andras
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