Other
Scientific paper
Nov 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt........21g&link_type=abstract
Thesis (PhD). UNIVERSITY OF KANSAS, Source DAI-B 61/04, p. 2011, Oct 2000, 201 pages.
Other
Scientific paper
Between 1990 and 1993 the Ulysses space probe observed approximately 160 collisionless interplanetary shocks. A shock is defined here as a rapid transition from one plasma and interplanetary magnetic field state to another. Among these was a shock occurring on March 23, 1991. One of the salient features of this shock was complicated angular (non-gyrotropic) distributions of energetic ions that occurred while particles were interacting with the shock. Using HISCALE data, a careful analysis was made of seven quasi-perpendicular shocks whose pitch angle distributions exhibited clear evidence of a non-gyrotropic anisotropy. We developed a procedure to analyze the direction and magnitude of the anisotropy, and to investigate a relationship between the direction of the anisotropy and the direction of the shock normal. The non-gyrotropic feature in the PAD's indicates that there is a gyro-phase dependent intensity. Using the fact that the count rates are functions of the pitch angle and phase angle, we expanded the energetic particle count rates in a series of spherical harmonics. Using the resulting function for the count rates, we determined (1)the amplitude of the anisotropy, (2)the direction of the anisotropy in terms of the phase angle, 4 , and (3)we evaluated the count rate, R( a,4 ), at non-tabulated values of pitch and phase angle. Analysis of the density gradient for three of the shocks showed that, in the region of the shock crossing, the phase angle of the transverse anisotropy, 4ext , is nearly equal to the shock normal angle, qbn . We also showed that for these shocks, the actual gradient lies in the plane containing the shock normal and the upstream magnetic field. By showing that the directions of the gradients in particle density are controlled by the shock geometry, we have established another aspect of the shock acceleration of charged particles. A further result is to establish the usefulness of charged particle anisotropies as a tool for the analysis of shock geometry.
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