Statistics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsh12a..01w&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SH12A-01
Statistics
7807 Charged Particle Motion And Acceleration, 7811 Discontinuities, 7851 Shock Waves, 2154 Planetary Bow Shocks, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
A quarter century of study has led to a characterization of the wave domains and particle properties of the terrestrial foreshock. Numerous factors might be expected to affect the upstream ion production, including shock geometry, the absence or presence of waves, and possibly the connection of foreshock field lines with the magnetopause. To date, the greatest emphasis has been on θ Bn = cos-1(B \cdot n/| B \cdot n|), where B is the interplanetary magnetic field (IMF) and n is the bow shock normal inferred for the particle source region. Little effort has been made to control for another important geometric parameter, θ vn = cos-1 vsw \cdot n/|vsw \cdot n|), with vsw the solar wind velocity. Consequently earlier statistical results have convolved effects and failed to reveal some trends. Here we present results from a study focusing on emergent field-aligned beams when significant local ultra-low freqency waves were absent. We have minimized the effects of θ vn variation by considering individual foreshock transits due to rotations of the IMF over intervals for which the position of the spacecraft relative to the shock source remained nearly constant. Unusual care has been taken to remove instrument noise and the tail of the solar wind beam, allowing us to consider very low speed and density beams in our statistics. Results include a strong inverse dependence of upstream ion density with θ Bn, and a change in the slope of this trend between 40--50° . Velocities show a linear dependence upon cosθ Vn/cosθ Bn, consistent with simple reflection kinematics, but the magnitude of the slope can be larger than models predict. The observed ratio of perpendicular to parallel temperature around 4 is expected, but often there is little dependence of either temperature on θ Bn. The theory for field-aligned beam production is far from definitive, and these observations provide new constraints.
Dandouras Iannis
Lucek Elizabeth
Mazelle Christian
Meziane Karim
Parks George K.
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