Abstract
We have used Advanced Composition Explorer instruments to survey the period 2007 March through the end of 2008 for ^3He-rich solar energetic particle (SEP) events occurring during near solar minimum conditions. Four events were found, all associated with single solar active regions in the western hemisphere. They all show ^3He:^4He ratios of a few percent (i.e.,≳100 times solar system abundances), low intensities, and spectra extending up to at least 1 MeV nucleon^(–1). Two events, on 2008 February 4 and 2008 June 16, were devoid of signatures associated with ^3He-rich SEPs, namely they lacked associations with energetic electrons and type-III bursts. In addition, there were no clear coronal mass ejections and X-ray flare activity was very low or absent. We take this as evidence that the irreducible requirement for ^3He-rich SEPs is a western hemisphere solar active region where magnetic and plasma processes preferentially energize ^3He and heavy ions.
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