HR: 16:00h
AN: SM54A-01 [Abstracts]
TI: A Solar Wind Input Parameter Based on Dipole Tilt Considerations
AU: * Bargatze, L F
EM: lfb@igpp.ucla.edu
AF: Institute of Geophysics and Planetary Physics, Box 951567
University of California, Los Angeles, Los Angeles, CA 90095-1567
United States
AU: Walker, R J
EM: rwalker@igpp.ucla.edu
AF: Department of Earth and Space Sciences, Box 951567
University of California, Los Angeles, Los Angeles, CA 90095-1567
United States
AU: Walker, R J
EM: rwalker@igpp.ucla.edu
AF: Institute of Geophysics and Planetary Physics, Box 951567
University of California, Los Angeles, Los Angeles, CA 90095-1567
United States
AU: McPherron, R L
EM: rmcpherron@igpp.ucla.edu
AF: Department of Earth and Space Sciences, Box 951567
University of California, Los Angeles, Los Angeles, CA 90095-1567
United States
AU: McPherron, R L
EM: rmcpherron@igpp.ucla.edu
AF: Institute of Geophysics and Planetary Physics, Box 951567
University of California, Los Angeles, Los Angeles, CA 90095-1567
United States
AB:
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.
DE: 2700 MAGNETOSPHERIC PHYSICS (6939)
DE: 2722 Forecasting (7924, 7964)
DE: 2723 Magnetic reconnection (7526, 7835)
DE: 2784 Solar wind/magnetosphere interactions
DE: 2788 Magnetic storms and substorms (7954)
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005