3He rich periods measured by the Suprathermal Ion Telescope (SIT) on STEREO-A during solar cycle 24

<p><sup>3</sup>He-rich solar energetic particle (SEP) events are characterized by a peculiar elemental composition with rare species like <sup>3</sup>He or ultra-heavy ions tremendously enhanced over the solar system abundances.<br>We report on <sup>3</sup>He rich SEP periods measured by the Suprathermal Ion Telescope (SIT) onboard STEREO-A beginning in 2007 until 2020, covering the whole solar cycle 24.<br>The mass resolution capabilities of SIT do not allow to easily distinguish between <sup>3</sup>He and <sup>4</sup>He especially in cases of a low <sup>3</sup>He to <sup>4</sup>He ratio.<br>We therefore developed a semi-automatic detection algorithm to find time periods during which a <sup>3</sup>He enhancement can be statistically determined.<br>Using this method we found 112 <sup>3</sup>He rich periods.<br>These periods were further examined in regards of their <sup>3</sup>He/<sup>4</sup>He and Fe/O ratio. <br>Previously about ten <sup>3</sup>He-rich SEP periods measured by SIT on STEREO-A have been reported.<br>An association with in-situ electron measurements by STEREO-SEPT and STEREO-STE showed that ~60% of the 112 periods are accompanied with electron events.<br>The here presented catalogue of <sup>3</sup>He rich periods is intended to serve as a reference for the community.</p>