Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm54a..01b&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SM54A-01
Physics
2700 Magnetospheric Physics (6939), 2722 Forecasting (7924, 7964), 2723 Magnetic Reconnection (7526, 7835), 2784 Solar Wind/Magnetosphere Interactions, 2788 Magnetic Storms And Substorms (7954)
Scientific paper
The objective of this study is to examine directly whether the interplanetary magnetic field (IMF) Bx component plays a role in solar wind-magnetosphere coupling. Researchers tacitly assume that Bx exerts little if any control over the interaction because the transverse components of the IMF are amplified upon passage through the sub-solar bow shock and because Bx is nearly perpendicular to the Earth's dipole axis. The most commonly used solar wind input parameters are constructed by using the solar wind velocity (to some power) multiplied by a function based on the transverse components of the IMF, By and Bz and by a gating function that accounts for the rectified nature of magnetospheric response. Our approach recognizes that a component of Bx projects on the dipole direction when the dipole tilt angle, Ψ, is non-zero. Thus, one can compute a cognate for commonly used input parameters such as VBs to account for the possibility of Bx-dipole tilt control via simple geometric arguments: VBeff=V[Bzcos(Ψ)-fBxsin(Ψ)]s. Here, the coefficient f is a factor that would be equal to 0.25 if the IMF transverse components were to always increase fourfold at the bow shock. The subscript "s" appearing at the end of the equation denotes that a VBs-style rectifying function has been applied to the sum appearing within the square brackets. If f is set equal to 1.0, the equation for VBeff essentially reduces to measuring VBs in SM coordinates instead of GSM coordinates. Cross-correlation and linear prediction filter tests have been performed by using interplanetary observations to calculate long-term time series for new input parameters that include the Bx-dipole tilt effect. To date, the results show that correlation coefficients found when analyzing VBeff along with AL or PC index time series are equal to or some 10% greater than corresponding correlation coefficients found by using VBs. The results also indicate that the factor f found via empirical testing may be larger than 0.25 suggesting that field line draping upstream of the magnetopause may enhance the influence of Bx on coupling. Further testing is required to establish whether these results are general. If proven true, the implications on our understanding of solar wind-magnetosphere coupling would be broad. For instance, they suggest that reconnection between sheath and magnetospheric field lines most likely occurs at the magnetic equator instead of the sub-solar region. Inclusion of Bx controlled coupling would also impact recent arguments concerning explanation of the Russell-McPherron seasonal variation of geomagnetic activity.
Bargatze L. F.
McPherron Robert L.
Walker Ray J.
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