Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh72b..05z&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SH72B-05
Other
2114 Energetic Particles, Heliospheric (7514), 2118 Energetic Particles, Solar, 2134 Interplanetary Magnetic Fields
Scientific paper
One of surprising discoveries by Ulysses at high heliographic latitudes during the 2000-2001 solar maximum is that essentially all the large gradual solar energetic particle events can be observed at Ulysses and Earth simultaneously despite their large separation in longitude and latitude. The particle fluxes at the two locations often become comparable within a few days after the onset and the fluxes often remain comparable for several weeks during the decay phase of the solar energetic particle events. These observations suggest that energetic particles can transport across heliographic longitude and latitude fairly easily, or that the particle sources extend considerably in latitude and longitude. In the paper, we present compelling evidence, obtained from the analysis of anisotropy measurements of the Bastille Day 2000 solar particle event and other events, for substantial transport of fast 40-90 MeV solar energetic protons across the local magnetic field. The large source extent in latitude is not necessary to explain the observations. The observed anisotropy of the particle intensity is often directed at significant angles (sometimes 90 degrees) to the measured magnetic field direction for periods of many hours, and its magnitude exceeds 10% (sometimes 50%), which is much too large to be accounted for by the Compton-Getting effect. The anisotropy direction is not correlated with the polarity of the magnetic field. We believe the observation can only be explained as cross-field diffusion flow in the presence of a particle gradient. A simple diffusion model is found to fit the direction of particle flows with a large inferred kappa perpendicular to kappa parallel ratio of as much as 25%. Similar large values of this ratio were found from observations of energetic particles in association with corotating interaction regions at low latitudes (Dwyer et al., 1997).
Jokipii Randy J.
McKibben Bruce R.
Rassoul Hamid K.
Zhang Minghui
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