Characteristic Times of Gradual Solar Energetic Particle Events and Their Dependence on Associated Coronal Mass Ejection Properties

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Abstract : We use 20 MeV proton intensities from the EPACT instrument on Wind and coronal mass ejections (CMEs) from the LASCO coronagraph on SOHO observed during 1998-2002 to statistically determine three characteristic times of gradual solar energetic particle (SEP) events as functions of solar source longitude: (1) T(sub 0), the time from associated CME launch to SEP onset at 1 AU, (2) T(sub R), the rise time from SEP onset to the time when the SEP intensity is a factor of 2 below peak intensity, and (3) T(sub D), the duration over which the SEP intensity is within a factor of 2 of the peak intensity. Those SEP event times are compared with associated CME speeds, accelerations, and widths to determine whether and how the SEP event times may depend on the formation and dynamics of coronal/interplanetary shocks driven by the CMEs. Solar source longitudinal variations are clearly present in the SEP times, but T(sub R)and T(sub D) are significantly correlated with CME speeds only for SEP events in the best-connected longitude range. No significant correlations between the SEP times and CME accelerations are found except for T(sub D) in one longitude range, but there is a weak correlation of T(sub R) and T(sub D) with CME widths. We also find no correlation of any SEP times with the solar wind O(exp +6)/O(exp +7) values, suggesting no dependence on solar wind stream type. The SEP times of the small subset of events occurring in interplanetary CMEs may be slightly shorter than those of all events.