Coronal Holes, Jets, and the Origin of 3He-rich Particle Events

Using magnetograph measurements, coronal field extrapolations, and imaging observations, we investigate the solar origins of 25 ³He-rich particle events from the period 1997-2003. In essentially every case we find that the source of the impulsive solar energetic particles (SEPs) lies next to a coronal hole containing Earth-directed open field lines. Averaged over all events, the source-hole separation is only ~4° at the photosphere. The source itself is typically a small, flaring active region located between longitudes ~W25 and ~W72. Around the estimated particle injection time, EUV images often show a jetlike ejection aligned with the open field lines. In some cases, a corresponding white-light jet is seen at heliocentric distances >~2 R_solar, similar to those studied earlier by Wang & Sheeley. The jets show a tendency to recur, a behavior that is reflected in the time variation of the measured ³He and Fe particle intensities. We interpret the jets as signatures of magnetic reconnection (``footpoint exchange'') between closed and open field lines. On the basis of these findings, we expect ³He enrichments to be observed whenever Earth-connected open field lines undergo footpoint exchanges with nearby active or ephemeral region fields. Because small bipoles emerge continually inside coronal holes, moderate enhancements in the ³He level can occur even when no significant flaring activity is recorded.