摘要
Based on multiple-spacecraft observations, we select 157 gradual solar energetic particle (SEP) events spanningfrom 2007 January to 2017 October. These SEP events are classified into Fe-rich and Fe-poor events inaccordance with their event-integrated Fe/O ratio (relative to the coronal reference value of 0.131). Acomparative analysis is performed to investigate the correlationship between SEP properties and the associatedsolar eruptions for these two classes of events, aiming to reveal the impacts of different seed populations on SEPevents. The main conclusions are as follows: (1) Fe-rich events are generally associated with coronal massejections (CMEs) that have lower speed, mass, kinetic energy, and lower-class flares, along with lower peakfluxes, in comparison to Fe-poor events. Moreover, there is no significant correlation between the peak intensitiesof Fe-rich events and CME speeds. In contrast, the peak intensities of Fe-poor events exhibit a strong positivecorrelation with CME speeds, and they encompass nearly all (96%) extremely large SEP events. (2) The pre-CMEs (preceding CMEs occurring within 24 hr prior to the primary CME associated with SEP event) associatedwith both Fe-rich and Fe-poor events show no significant difference. However, the occurrence rate of Fe-richevents slightly increases with more frequent pre-CME eruptions. The occurrence rates of the two classes of SEPevents associated with different type-Ⅱ radio bursts exhibit distinct differences: the occurrence rate of Fe-richevents decreases progressively from the metric (m), to the decameter-hectometric (DH), and then to the kilometric(km) wavebands. This may imply that the dominant seed particles accelerated by the shock have undergonechanges at different altitudes, for instance, from flare materials with a high Fe/O ratio to coronal/solar windmaterials with a low Fe/O ratio. (3) The two classes of SEP events display distinct longitudinal distributions andeast-west asymmetries. The occurrence rate of Fe-rich events reaches their maxima within the relativelongitudinal range of 30°–90° indicating the degrees of the source westward of the magnetic footpoint, which isparticularly pronounced in the case of medium- or low-speed CMEs. At various relative longitudes, the peakintensities of the two classes of SEP events also show statistically significant differences, with the Fe-poor eventtypically exhibiting a notably higher intensity compared to the Fe-rich event.
基金
supported by the National Natural Science Foundation of China(grant No.42274215)
the“333”High-Level Talent Cultivation Project of Jiangsu Province,China.
