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Abstract

³He-rich solar energetic particles (SEPs), showing up to a 10,000-fold abundance enhancement of rare elements like ³He or ultra-heavy nuclei, have been a puzzle for more than 50 years. One reason for the current lack of understanding of 3He-rich SEPs is the difficulty resolving the source regions of these commonly occurring events. Since their discovery, there has been strong evidence that ³He-rich SEP production is associated with flares on the Sun. Anomalous abundances of ³He-rich SEPs have been attributed to a unique acceleration mechanism that must routinely operate at flare sites. Flares associated with ³He-rich SEPs have been often observed in jet-like forms indicating an acceleration in magnetic reconnection involving field lines open to interplanetary space. Owing to a fleet of spacecraft around the Sun, providing a greatly improved resolution of solar imaging observations, ³He-rich SEP sources are now explored in unprecedented detail. This paper outlines the current understanding of ³He-rich SEPs, mainly focusing on their solar sources.