Abstract: Solar Energetic Particles (SEPs), especially for gradual and large (flux of ions with energy >10 MeV above 10 pfu) SEP events, play an important role in space weather effects as they may pose major radiation hazards for spacecraft and astronauts. Understanding the acceleration, release, and transport of SEPs in the heliosphere is one of the outstanding problems in heliospheric physics, and thus has been investigated for a long time. Since the 21st century, combining advanced observations from multiple viewpoints and in multiple wavelengths, we are able to further dig into the SEP studies.
In this presentation, we start from gradual and large SEP events which are believed to be produced by shocks associated with fast and wide Coronal Mass Ejections (CMEs). The scattering of the relationship between the SEP peak intensities and CME speeds in statistics suggests a scenario that a fast primary CME is preceded by previous CMEs is favorable to a more efficient particle acceleration (twin-CME scenario). We investigate the role of CME-CME interaction in the acceleration and release of SEPs in detail. In the twin-CME scenario, seed particle populations, which act as an important factor in the shock acceleration mechanism of energetic particles, are thought to be enhanced by preceding CMEs. We further analyze the roles of CME-CME interaction and other associated factors (e.g., magnetic connectivity, CME speed, flare size, and seed particle background) by incorporating SEP-poor events. The results show that in a statistical sense, the consideration of seed populations cannot improve the prediction of SEP peak intensities. We note that these observations for SEPs and seed populations are limited near 1 au, while particle transport effects may not be neglected. The recently launched Parker Solar Probe (PSP) and Solar Orbiter (SolO) moving close to the Sun provide unique opportunities to investigate SEPs and seed populations in the innermost heliosphere. We then study a series of SEP events between 2021 May 27 and June 1 observed by PSP and STEREO-A at different heliocentric distances, and try to answer three questions on seed particle populations: (1) how long can they exist; (2) how widely can they extend/spread; and (3) how do they measured at 1 au correspond to those in the inner heliosphere? Finally, we discuss a question/debate about the acceleration and release of SEPs in association with the coronal EUV wave (which may correspond to the footpoint of CME-driven shocks on the solar surface) based on an SEP event observed by SolO, PSP, STEREO-A, and L1 spacecraft at different locations.
Hosted by Yi-Hsin Liu and Xiaocan Li
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Meeting ID: 927 5142 0885