Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999dps....31.7303d&link_type=abstract
American Astronomical Society, DPS meeting #31, #73.03
Astronomy and Astrophysics
Astronomy
Scientific paper
A comparison of radio observations with models on enhanced radial diffusion and direct shock acceleration show that most of the observed phenomena can be explained. Initially, there is a sudden, million-fold, increase in the radial diffusion coefficient, a number determined from estimates derived from self-consistent calculations of the electromagnetic turbulence generated by the impacts. Under these circumstances assumptions based upon a drift-averaged behavior of electrons is no longer valid (i.e., we use the local rather than drift loss cone). The largest enhancements in intensity and largest inward shift of the radiation peaks are calculated to occur at jovicentric longitudes 100 - 250 deg., i.e., the longitude range where the B= constant contours are furthest from the planet, and the local loss cone is smallest. This longitude range does agree with the region where most of the enhancements have indeed been observed. The diffusion models show that the main radiation peaks brighten up much more than the high latitude regions, as is indeed observed during the first few days of the impact week. The dramatic increase in the intensity of the high latitude peaks later in the week is attributed to a direct acceleration of electrons by the upward propagating shock. Only after the ionosphere has been modified by several impacts (so that the Alfv{\' e}n velocity is decreased through massloading, e.g., by dust) is it feasible for the shock to propagate through the ionosphere into the magnetosphere, and interact directly with the magnetospheric particles close to the impact site. We show calculation of this effect. Finally, compared to the observations, the radial diffusion models predict much larger enhancements in the radiation peaks than what is observed, which we attribute to a large loss of electrons due to pitch angle scattering.
Brecht Stephen H.
de Pater Imke
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