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Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm11b0434b&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM11B-0434
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2724 Magnetopause, Cusp, And Boundary Layers, 2752 Mhd Waves And Instabilities, 2784 Solar Wind/Magnetosphere Interactions, 3210 Modeling : : : : : : : : : : : : : : :, 2134 Interplanetary Magnetic Fields, 2149 Mhd Waves And Turbulence, 2164 Solar Wind Plasma
Scientific paper
Although interplanetary magnetic field (IMF) vectors near the Earth are on average lying near the ecliptic plane, there is often a significant Bz component, which is important for the development of geomagnetic activity. Two main causes are thought to be responsible for the generation of IMF Bz: an inherent magnetic field existing inside plasma clouds in the solar wind, and 3-D disturbances of the ambient magnetic field by moving plasma inhomogeneities (due to draping of the ambient magnetic field around plasma inhomogeneities). The former mechanism links the IMF Bz to new plasma with a frozen-in magnetic field while the latter one assumes the formation of IMF Bz to take place in ambient plasma as an effect of, for instance, approaching high-speed plasma flows. In the first case the plasma density per unit magnetic flux (the n/B parameter) may vary in an arbitrary way while in the second case the n/B parameter should be approximately constant. This allows us to try to estimate relative contributions to IMF Bz generation from these two mechanisms. For this purpose we carried out a statistical study of hourly IMF variations for three years 1998-2000. We provided a cross-correlation analysis for variations IMF Bz with Bx, By, and the value of horizontal magnetic field vector Bxy for different values of n/B (which is a freezing-in parameter). We found high correlation for IMF Bz and By and lower correlation for Bz and Bx, but the best correlation was observed for variations of Bz and Bxy. For all cases the correlation was out of phase: increasing Bz was associated with decreasing other IMF components that is consistent with predictions from the draping mechanism. Correlation coefficients increased strongly with decreasing n/B factor. For Bz versus Bxy and n/B = 0.1, the correlation coefficient was higher than 0.6 that says in favor of high effectiveness for the formation of Bz field by moving plasma inhomogeneities from horizontal magnetic field components. This effect increases with increasing solar wind speed and for small angles of IMF vector to Sun-Earth line. We also compared the obtained results with expected 3-D variations in the magnetic field appearing because of draping magnetic field lines about a moving plasma ball and inclined cylinder (the last case is related to high-speed stream in the solar wind). The experimental results are well consistent with predictions from these simple models but the better agreement takes place for inclined plasma cylinder.
Bender Laurence
Farrugia Charles J.
Gnavi Graciela
Gratton Fausto T.
Lyatsky Wladislav
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