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Shock Geometry and Spectral Breaks in Large SEP Events

Li, G. and Zank, G. P. and Verkhoglyadova, Olga and Mewaldt, R. A. and Cohen, C. M. S. and Mason, G. M. and Desai, M. I. (2009) Shock Geometry and Spectral Breaks in Large SEP Events. Astrophysical Journal, 702 (2). pp. 998-1004. ISSN 0004-637X. doi:10.1088/0004-637X/702/2/998.

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Solar energetic particle (SEP) events are traditionally classified as "impulsive" or "gradual." It is now widely accepted that in gradual SEP events, particles are accelerated at coronal mass ejection-driven (CME-driven) shocks. In many of these large SEP events, particle spectra exhibit double power law or exponential rollover features, with the break energy or rollover energy ordered as (Q/A)^α, with Q being the ion charge in e and A the ion mass in units of proton mass m_p . This Q/A dependence of the spectral breaks provides an opportunity to study the underlying acceleration mechanism. In this paper, we examine how the Q/A dependence may depend on shock geometry. Using the nonlinear guiding center theory, we show that α ~ 1/5 for a quasi-perpendicular shock. Such a weak Q/A dependence is in contrast to the quasi-parallel shock case where α can reach 2. This difference in α reflects the difference of the underlying parallel and perpendicular diffusion coefficients κ_(||) and κ ⊥. We also examine the Q/A dependence of the break energy for the most general oblique shock case. Our analysis offers a possible way to remotely examine the geometry of a CME-driven shock when it is close to the Sun, where the acceleration of particle to high energies occurs.

Item Type:Article
Related URLs:
URLURL TypeDescription
Li, G.0000-0001-9313-251X
Zank, G. P.0000-0002-4642-6192
Verkhoglyadova, Olga0000-0002-9295-9539
Mewaldt, R. A.0000-0003-2178-9111
Cohen, C. M. S.0000-0002-0978-8127
Mason, G. M.0000-0003-2169-9618
Desai, M. I.0000-0002-7318-6008
Additional Information:© 2009. The American Astronomical Society. Received 2009 February 1; accepted 2009 July 9; published 2009 August 18. This work is supported in part by NASA grants NNX06AC21G, NNH07ZDA001N-HGI and NNX07AL52A for G.L., O.V., and G.P.Z. at UAH; NNX06AC21G, NNX8AI11G, and NNX07AP69G for RAM and CMSC at Caltech; Caltech subcontract 44A-1081056 for G.M.M. at A.P.L., and NNH07ZDA001N-HGI for M.I.D. at SWRI. The authors acknowledge discussions with M.A. Lee and an anonymous referee for valuable comments. G.L. thanks Dr. Yan Wang for some very stimulating discussions.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Subject Keywords:acceleration of particles; Sun: coronal mass ejections (CMEs)
Issue or Number:2
Record Number:CaltechAUTHORS:20090917-150452855
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Official Citation:Shock Geometry and Spectral Breaks in Large SEP Events G. Li, G. P. Zank, Olga Verkhoglyadova, R. A. Mewaldt, C. M. S. Cohen, G. M. Mason, and M. I. Desai 2009 ApJ 702 998-1004 doi: 10.1088/0004-637X/702/2/998
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15930
Deposited On:18 Sep 2009 23:00
Last Modified:08 Nov 2021 23:23

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