Physics – Plasma Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh34a..03n&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH34A-03
Physics
Plasma Physics
[7514] Solar Physics, Astrophysics, And Astronomy / Energetic Particles, [7845] Space Plasma Physics / Particle Acceleration, [7851] Space Plasma Physics / Shock Waves, [7867] Space Plasma Physics / Wave/Particle Interactions
Scientific paper
The 2011 March 21 solar energetic particle (SEP) event is strong at STEREO-A and weak at Earth L1 Lagrangian point, with quite different intensity time histories and energy spectra. Details of the SEP, flare, CME and in situ plasma and field observations are presented by Rouillard et al. at this conference. Here we report on our modeling of the transport of multi-species SEPs coupled to Alfvén-wave amplification by streaming energetic protons. The pre-shock proton intensity observed by IMPACT at STEREO-A is averaged over 21 hours after the fast rise. This "plateau" intensity spectrum flattens below 2 MeV at a few 100 pfu, where 1 pfu = protons/(cm^2 s sr MeV). By contrast, at 90 deg to the east, spacecraft at L1 observe a slow and small intensity rise with power-law spectra while, 90 deg even further east, STEREO-B observes no significant increase. Modeling SEP transport in this event requires quite different energy- and time-dependent release of accelerated SEPs at the traveling shock on the different field lines leading to STEREO-A and L1. We infer that the shock accelerated a large number of > 3 MeV protons on field lines leading to STEREO-A. The numerous protons generate strong wave growth, which limits the proton intensity and flattens the energy spectrum at < 2 MeV. In contrast, on field lines leading to L1, the shock accelerated far fewer energetic protons, which amplified few waves. With few self-amplified waves to "trap" the SEPs near the shock, the proton intensity rises toward low energy as a power law. This finding from observations at two widely separated spacecraft in the same SEP event is consistent with the conclusion of our comparative modeling of the weak 1998 May 2 and strong 2003 October 28 ground level events. Together, these four event observations show a progression from weak shock acceleration and power-law intensity spectrum at ~ 1 AU to strong shock acceleration and a flattened energy spectrum. As shock acceleration to proton intensity > 100 pfu increases its range from < 7 MeV to < 50 MeV going from the 2011 March 21 event at STEREO-A to the 2003 Oct 28 event at L1, the energy of spectral flattening rises from 2 MeV to 20 MeV. We will also present fitting of the observed intensity and spectra of minor ions. We thank Glenn Mason for his advice on ACE/ULEIS observations. Work at GSFC is funded by NASA. Work of APR was partly funded by NASA contracts NNX11AD40G-45527 and NNXIOAT06G. Work of CKN, DVR, and AJT are supported in part by NASA grants NNX09AU98G, NNX08AQ02G, and NNH09AK79I, respectively.
Ng Chee K.
Reames Donald. V.
Rouillard Alexis P.
Tylka Allan J.
von Rosenvinge Tycho T.
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