Statistical Research on the Longitudinal Distribution of Detected Properties of Solar Energetic Particles
2021, 41 (3):
Using the observations from multi-points spacecraft, e.g., SOHO and STEREO, 122 SEP events and associated CMEs during the 24th solar cycle from December 2006 to October 2017 are selected. The longitudinal distributions of SEP characteristics and their relationship with CMEs properties are analyzed, as well as the relation with the event-integrated Fe/O ratio. Results are shown as follows: Large SEP events usually have a lower Fe/O ratio, while those events with high Fe/O have lower CME velocity, mass and kinetic energy, but have faster flux rising speed. The duration Du and peak flux Ip of SEP correlate well with the associated CME velocity positively (correlation coefficient, CC: 0.50 and 0.57). Comparing to the events with a high Fe/O ratio, the events with low Fe/O obviously have much higher correlation coefficients for Du and Ip with CME. The characteristic time TO and TR of SEPs generally increases with the raising of relative longitude, while Du and Ip decrease distinctly with the raising of relative longitude. And the slope K of the SEPs flux enhancing in the onset phase seems to decrease from the east (-90°) to west (90°) relative to the source region. TO shows a negative correlation with CME velocity, mass and kinetic energy in the magnetic well-connected points, while there is no distinct correlation in other poor-connected points. Meanwhile, TR has a positive correlation with CME only in the relative longitude range of [-30°, +30°]. Du and Ip have a stronger correlation with CME velocity in the well-connected condition (CC: 0.60 and 0.75 respectively) than others (0.46 and 0.56). The conclusion reveals that the detection of SEP event and its time profile evolution is not only affected by the associated CME, but also controlled by the relative longitude between the magnetic foot point and the solar eruption source, and for the well-connected points, the detectable SEP event has more high intensity and good positive correlation with its associated CME, which is very important for the space weather prediction of SEP events, especially large or extremely large SEP events. Moreover, the SEP event with a high Fe/O ratio seems to become weaker among the relationship with CME, which implies that some facts such as flare acceleration, seed population, and so on, will play important roles during the generation of gradual SEP events associated with CME-driven shock.
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