Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm52a..04h&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM52A-04
Physics
2720 Energetic Particles, Trapped
Scientific paper
The recent SAMPEX report of prompt trapping of solar energetic Fe at L=2 in association with a Storm Sudden Commencement during the Bastille Day 2000 event leads to re-examining the necessary conditions for acceleration by a magnetopause compression-induced electric field impulse1. This storm also produced a new proton belt which formed on a diffusive time scale. New > 10 MeV electron and proton belts formed around L=2.5 on a drift time scale (minutes) during the March 24, 1991 SSC event, and were well-modelled by an azimuthal electric field impulse propagating in excess of the magnetosonic speed in the outer magnetosphere (2000 km/s assumed)2,3. Electrons and protons in drift resonance with this impulse were transported radially inward, requiring a source population which is multi-MeV at geosynchronous. A general requirement for such shock induced acceleration is a very high speed CME, with V > 1000 km/s at 1 AU, which launches a perturbation of comparable velocity inside the magnetosphere, perserving shock properties (radially confined electric and magnetic fields). Secondly, there must be a source population which is drift resonant. The CME-shock itself is a source of solar energetic particles, both protons and heavier ions, with higher fluxes and harder spectra associated with faster moving CMEs. For example, both the February 9, 1986 and March 24, 1991 events, with shock transit speeds of 1000-1400 km/s, produced prompt proton belts (L=2.8 and 2.5)4,5. The Bastille Day 2000 event provided an adequate source of drift resonant Fe at 2-4 MeV/nuc, but pre-shock arrival fluxes of 10 MeV protons were lower than for March 24, 1991, comparing GOES data at geosynchronous. The drift resonance condition of 1000-2000 km/s is more restrictive for the electron source population. While relativistic electron enhancements in the polar cap at 100 keV are sometimes associated with fast CME-shock events (February, 1986)4, the outer zone provides the most likely MeV source population, as was shown in the March 24, 1991 event simulation2. A relatively quiet period which allows for outer zone electron flux buildup and spectral hardening is a precondition favoring an event of this type. [1]Lorentzen et al., J. Geophys. Res., submitted, 2001. [2]Li et al., GRL, 20, 2423, 1993. [3]Hudson et al., GRL, 22, 291, 1995. [4]Gussenhoven et al., J. Geophys. Res., 94, 17121, 1989; IEEE Trans. Nuc. Sci., 36, 2008, 1989. [5]Blake et al., GRL, 19. 821, 1992.
Hudson Mary K.
Lorentzen K. R.
Lyon John G.
Mazur J. E.
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