Solar source longitudinal dependence of SEPs and their association with solar flares and radio-loud CMEs

Abstract

In this article we examine the occurrence probability of 104 major (Ip, at energies > 10 MeV) solar energetic particle events (SEPs) and their peak intensity dependence on source longitude and on the characteristics of solar flares/radio-loud (RL) coronal mass ejections (CMEs) during the period November 1997–December 2014. We classified them into three sets of events based on the source longitude (L) of the associated solar flares: i) eastern side events (30°E < L ≤ 90°E), ii) disk center (30°E ≤ L ≤ 30°W), and iii) western side events (30°W < L ≤ 90°W). On average, the mean rise time and duration of SEPs are significantly larger for eastern side events (2168 min and 4.16 days, respectively) than the disk center (1338 min and 2.65 days, respectively) and western side events (662 min and 2.42 days, respectively). The mean peak intensity of SEPs from the disk center (10^3.56 pfu) is found to be greater than that of SEPs from the western (10^2.88 pfu) and eastern (10^2.53 pfu) sides, respectively. The western side events (54%) have significantly higher occurrence probability than the disk center (34%) and eastern side (12%). While there is no significant difference in most of the properties of solar flares and RL CMEs, the eastern side associated RL CMEs are highly decelerated (‑29.37 m s^‑2) than the disk center (‑17.44 m s^‑2) and western side (‑9.09 m s^‑2) events. The relationship between peak intensity of SEPs and peak flux of solar flares shows that the correlation coefficients (cc) decrease from the eastern side to the western side: 0.65 (eastern), 0.51 (disk), and 0.35 (western). Interestingly, we found that there is a good correlation between the peak intensity of major SEPs and the speed of the CMEs (cc=0.75) for disk center. From this study, we have concluded that gradualness depends on source longitude and increases from western to eastern side. It is also inferred that the relationship of peak intensity of SEP events with solar flare flux/CME speed is strongly dependent on source longitude.