Effect of magnetic discontinuities on the propagation of energetic particles: Ulysses observations of the onset of the March 1991 solar particle event

Details Effect of magnetic discontinuities on the propagation of energetic particles: Ulysses observations of the onset of the March 1991 solar particle event Effect of magnetic discontinuities on the propagation of energetic particles: Ulysses observations of the onset of the March 1991 solar particle event

Aug 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000jgr...10518275s&link_type=abstract

Journal of Geophysical Research, Volume 105, Issue A8, p. 18275-18284

Astronomy and Astrophysics

Astrophysics

8

Solar Physics, Astrophysics, And Astronomy

Scientific paper

We present observations of energetic ions from the Cosmic Ray and Solar Particle Investigation (COSPIN) and Heliospshere Instrument for Spectra Composition and Anisotropy at Low Energy (HISCALE) instruments on board the Ulysses spacecraft. We examine in detail the onset of energetic ions observed during the March 1991 series of solar events. Active region 6555, at E28 at 2247 UT on March 22, 1991 (day 81), was most likely responsible for the high-energy protons subsequently seen at Ulysses. A slow increase in the high-energy (~50 MeV) proton intensity, made up of many small but rapid intensity increases, began around 9 hours after the onset of the event, taking 1.5 days to reach maximum intensity. On the flank, and in front of a coronal mass ejection (CME), coming from a previous event, we observed a region with a drop in the magnetic field strength. This region was populated with hot shocked plasma and, owing to the low magnetic field pressure, had an ion plasma beta >1. Mirror mode waves, with discontinuities appearing at the edges of the waves, produced a larger-than-average number of magnetic field discontinuities, a large fraction of the discontinuities being aligned with their normals oriented along the radial direction, suggesting that they were being convected outward by the CME. These discontinuities acted as a series of barriers to the propagation of the energetic solar particles coming from the solar event, delaying substantially the onset of the particle event at Ulysses.

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