A Study of the Conditions that Can Lead to the Production of 3He-rich SEP Events Having Broad Longitudinal Extents

Abstract:

Source regions for 3He-rich solar energetic particle (SEP) events detected 1 AU from the Sun are typically found within ~20-30 degrees of the footpoint of the field line connecting the observer to the corona. However, some events have been detected by multiple spacecraft at significantly greater longitudinal separations. The broadest event (7 Feb 2010), which may be attributable to perpendicular transport caused by scattering in the interplanetary medium, shows a strong decrease of detected 3He fluence with increasing separation from the best connected field line. On the other hand, an event that occurred on 2 May 2014 under conditions of minimal interplanetary scattering appears to be the result of a large expansion of the active-region field between the photosphere and the source surface. In this event, similar 3He intensities were detected at locations separated by 38 degrees. These observations suggest correlations among the field expansion in the corona and fluence variations between observation points at 1 AU. We report results of a study in which the coronal spreading inferred from potential source surface field (PFSS) maps is compared with measured fluence ratios to establish the extent to which the spreading mechanisms inferred in these two prototypical events are applicable the the larger population of 3He-rich SEP events observed in the era of multispacecraft observations.