Solar Energetic Particles and Interplanetary Type III Bursts

Abstract:

Reliable forecasting of solar energetic particles (SEPs) is difficult due to the near-relativistic speeds of the highest energy particles, uncertainty how they are accelerated and transported, including their poorly-understood longitudinal spread. We investigate a possibility to improve SEP forecasting using space-based radio instrumentation. Type III radio bursts are intense radio emissions triggered by beams of energetic electrons often associated with solar flares. These exciter beams propagate outwards from the Sun along open magnetic field lines in the corona that extend into the interplanetary medium. A majority (nearly 100%) of the SEP events measured in situ are associated with interplanetary type III bursts, but there are also many type III bursts that are not associated with SEP events observed in situ. We investigate temporal and spatial correlations between solar flares, type III bursts, and SEP events for several historical events, focusing on NOAA storm category S2 and larger. We discuss the possible need for real-time interplanetary radio observations, including direction-finding, a capability that currently does not exist, to be included on future missions to enhance SEP forecasting.