High-Energy Proton Intensity Enhancements Associated with the Passage of Interplanetary Shocks

Abstract:

We analyze periods with elevated >40 MeV proton intensities observed at 1 AU over the last 4 solar cycles (1973-2020) that coincide with the passage of interplanetary shocks. Commonly, these elevated proton intensities result from large solar energetic particle (SEP) events. The interplanetary shocks observed during these elevated-intensity periods may or may not be related to the origin of the SEP events. Usually, the passage of an unrelated shock is not associated with any changes in the high-energy proton intensities or in the evolution of the SEP event. However, occasionally, such shocks produce local particle increases that may extend to very high-energies, even above 100 MeV. The particle enhancements associated with the passage of shocks related to the origin of the SEP events are known as “energetic storm particle” (ESP) events. ESPs may result from [1] local particle acceleration at the shock, [2] particle acceleration in the compressed turbulent post-shock region, and/or [3] particles confined in the vicinity of the shock by either ambient solar wind structures, magnetic field fluctuations amplified by the shock-accelerated particles, or by turbulent post-shock fields. We will present examples of high-energy (>100 MeV) ESP events most likely resulting from local shock particle acceleration, and other cases where the high-energy particle enhancements result from the effects produced by ambient solar wind structures such as intervening interplanetary coronal mass ejections. Such high energy proton intensity enhancements associated with shocks are of interest because they can be the dominant contributor to the high energy proton population in some SEP events, with particles accelerated in the early stages of the event close to the Sun making a smaller contribution.