High Energy Solar Particle Events and their Associated Coronal Mass Ejections

Abstract

Intense solar energetic particle (SEP) events data, associated with ground level enhancements (GLEs), occurred during 1989 to 2006 have been obtained from the spectrometers on board GOES spacecraft in the energy range 10-100 MeV. The interplanetary effects of these events and their associated coronal mass ejections (CMEs) have been provided by the LASCO/SOHO coronagraph images in the field of view of 2-30 {\rsun} and the interplanetary scintillation images from the Ooty Radio Telescope in the heliocentric distance range of $\sim$40-250 R$_\odot$. The comparison between the radial evolution of the CME and its associated particle spectrum shows that the spectrum is soft at the onset of the particle event. A flat spectrum is observed at the peak of the particle event and the spectrum becomes steeper as the CME moves farther out into the inner heliosphere. However, the magnitude of change in spectral slopes differs from one CME to the other, suggesting the difference in energy available within the CME to drive the shock. The spectral index evolution as a function of initial speed of the CME at different parts of the particle profile has also been compared. The result shows that the change in particle flux with time is rather quick for the high-energy portion of the spectrum than that of the low-energy part, which makes the steepening of the energy spectrum with time/distance from the Sun. It indicates that the acceleration of particles by a CME-driven shock may be efficient at low energies ($\leq$30 MeV) and the efficiency of the shock decreases gradually towards the high-energy side of the spectrum.Comment: 14 pages, 9 figures, 1 table; Submitted to Advances in Geosciences (Solar-Terrestrial Sciences