3He-rich and Other Solar Energetic Particle Events Observed on Solar Orbiter

Abstract:

One of the goals of the Solar Orbiter mission to the inner heliosphere is to understand how solar eruptions produce energetic particle radiation that fills the heliosphere. By observing these events from close to the Sun it will be possible to obtain insights not possible at 1 au, and as a result much of the mission's payload focuses on solar energetic particle (SEP) phenomena using a broad range of remote sensing and in situ observations that can identify the solar sites as well as their properties in the interplanetry medium including turbulence, shocks, and energetic particles. While large, CME-associated SEP events are not presently occurring during the solar minimum, there are nevertheless occasional impulsive, 3He-rich events that are typically associated with active regions bordering coronal holes that allow the particles to escape into interplanetary space. We report results from the Solar Orbiter Energetic Particle Detector/Suprathermal Ion Spectrometer (EPD/SIS) which covers the energy range~0.1-10 MeV/nucleon for H-Fe with high mass resolution. As of this writing one significant event was observed on 2020 July 21 with 3He/4He ~ 0.59, and will be discussed along with others that may occur later and compared with relevant observations at 1 au.