The characteristics of suprathermal electrons for small-scale magnetic flux rope events observed near 1AU

Abstract:

The small-scale magnetic flux rope events (SMFRs) have similar properties with large scale interplanetary flux ropes. However, the origin of SMFRs is not yet understood. The pitch angle distribution of suprathermal electrons ejected from the Sun flowing through the IMF field lines can give useful information about how the field lines connect to the Sun compared to the IMF polarity. In the present study we determined the characteristics of the suprathermal electrons during the SMFRs, which we have identified by applying the cylindrical force-free model to the published events (those observed by Wind spacecraft from 1995 to 2014 in Yu et al. (2016)). Out of the identified 261 SMFRs, we find that majority of the SMFRs (~45.2%) are associated with uni-directional beams, implying open field lines. The open field polarities are mostly associated with IMF sector structure. Only a much smaller percentage of the SMFRs (~10.6%) are associated with bi-directional beams. To determine if such bi-directional beams indeed imply closed field structure, we have investigated solar wind conditions around the bi-directional beam SMFRs. In addition, we also find a very small percentage (7.2%) of conic beam distributions during SMFRs. Lastly, the remaining ~37.0% of SMFR are associated with complex electron distributions. We will discuss implications of these statistics.