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Abstract:
We present results from a study of three SEP events that occurred on July 12, 2012, April 3, 2010, and March 15, 2013 to understand effects of the heliospheric current sheet (HCS) on the propagation of SEPs. The three SEP events are associated with coronal mass ejections (CMEs), which share a number of similar properties: all CMEs (1) were of halo type and were originated near the Sun-Earth line, (2) were fast (> ~1000 km/s initially), with similar Sun-to-Earth transit time, (4) were accompanied with shocks observed at 1 AU, and (4) induced large geomagnetic storms. However, the onset time and intensity of the SEP (~ 3–41 MeV/nuc. He) at 1 AU were quite different. Our magnetohydrodynamic simulations suggest that delays of SEP flux for the studied events are due to the presence of the HCS between the CME source and the observer. It is also shown that elevated SEP fluxes can occur after part of the CME expands into the same magnetic sector as the observer or the observer moved across the HCS. This study suggests that the HCS can limit the propagation of energetic particles, at least in the energy range studied here, in the heliosphere. * This work was supported partially by the Chief of Naval Research, NASA HSR & HTMS programs.
