Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm11b0436b&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM11B-0436
Physics
2149 Mhd Waves And Turbulence, 2722 Forecasting, 2728 Magnetosheath, 2784 Solar Wind/Magnetosphere Interactions, 7863 Turbulence
Scientific paper
The correlation between the amplitude of the MHD turbulence in the upstream solar wind and the amplitude of the Earth's geomagnetic-activity indices AE, AU, AL, Kp, ap, Dst, and PCI is explored. Increased amplitudes of the turbulence results in elevated geomagnetic indices. It is found that this "turbulence effect" accounts for about 100 nT of the variability of the AE index. The magnitude of the effect is the same for northward and for southward IMF. Tests are performed that conclude (1) that the turbulence effect is not caused by the turbulence amplitude acting as a proxy for |B| in the solar wind and (2) that reversals of the IMF from northward to southward in the turbulent fluctuations is not the cause of the correlations. An expression is derived for the total viscous-shear force on the surface of the magnetosphere; improved solar-wind/magnetosphere correlations result when this expression is used. The turbulence effect is interpreted as an enhanced viscous coupling of the solar-wind flow to the Earth's magnetosphere caused by an eddy viscosity that is controlled by the amplitude of MHD turbulence in the upstream solar wind: more upstream turbulence means more momentum transfer from the magnetosheath into the magnetosphere, resulting in more stirring of the magnetosphere, which produces enhanced geomagnetic-activity indices. The total energy input to the magnetosphere by this eddy-viscous coupling is theoretically estimated and compared with the data.
Borovsky Joseph E.
Funsten Herbert O.
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