SOHO/EPHIN observation of a multiple large solar energetic particles event in November 1997

Abstract

In November 1997, EPHIN (Electron, Proton, Helium INstrument) on board Solar and Heliospheric Observatory (SOHO 1 SOHO is a project of international cooperation between ESA and NASA. 1 ) detected solar energetic particles (SEP) from a multiple large event. Composition, temporal profiles and energy spectra of electrons, hydrogen and helium have been analyzed. The SEP events show, in general, gradual characteristics related to acceleration in the shocks driven the associated coronal mass ejections (CMEs). Composition features are very similar accounting that they are associated to the same active region and with similar physical conditions of the solar corona and solar wind. Temporal profile differences can be explained in terms of the different magnetic connection in both SEP events. During the November 6 SEP event the detection of some perturbations are produced by the passage of the shock and the halo CME associated with the November 4 event. Energetic characteristics of the SEP events denote differences between the November 6 SEP event, accelerated by a very fast shock, and the November 4 SEP event accelerated in a weaker shock. The compression ratio of the shock extracted from the SEP spectral index is correlated with the shock velocity reported and it demonstrates that protons and helium are accelerated by the same acceleration mechanism.