Schematic illustration of the various energetic particle populations in the heliosphere

Science Nuggets: Solar Energetic Particles

SEPs from the flare active region


Solar energetic particles (SEPs), with the energy ranges from a few keV to several GeV, are one population of particle streams produced by the rapid release of magnetic energy during solar eruptions. SEPs propagate to us over a great distance, carrying information in their energy spectra, element abundances, and ionization states. According to these information, we can have the knowledge of the properties of their source plasma and the physical mechanisms of their acceleration. In the past few decades, significant progress of the SEPs study has been archived in both observations and theories. However, the exact acceleration sources still remain enigmatic, especially in geo-effective or so-called major SEP events. The main controversy focuses on which process, flare or/and CME-driven shock, is dominant during the particle injection.

Magnetic reconnection rate compared with the microwave radio emissions.

Based on observations of particles and multi-wavelength emissions from both near-Earth spacecrafts and ground based neutron monitor, Li et al. (2009) present studies of SEPs dynamics (time history, spectrum and anisotropy), flare magnetic reconnection rate, and magnetic configuration above the active region in a major SEP event. The analytic results suggest that flare acceleration dominates the initial injection and produces strong anisotropic particles with a hard energy spectrum, and then the acceleration source changes to a wide-spread interplanetary CME-driven shock producing nearly isotropic particles with a soft energy spectrum.

For more details, see:

Li, C., Dai, Y., Vial, J. -C., Owen, C. J., Matthews, S. A., Tang, Y. H., Fang, C., and Fazakerley, A. N.
Solar source of energetic particles in interplanetary space during the 2006 December 13 event
A&A, 503, 1013 (2009)

 

This page was last modified 6 February, 2009 by cfo[at]mssl.ucl.ac.uk, cjo[at]mssl.ucl.ac.uk