Characterizing Solar Energetic Particle Event Profiles with Two-Parameter Fits

The intensity–time profiles of solar energetic (\(E>10~\mbox{MeV}\)) particle (SEP) events observed at 1 AU reflect a number of physical processes involving solar injection and interplanetary transport. In addition to energy spectral and composition studies, SEP intensity–time profiles are the basis for diagnostic timescales needed for describing and modeling the acceleration and transport of SEPs. We briefly review commonly used timescales and point out the absence of holistic descriptions of the SEP profiles. We define the requirements for such a description and select a modified Weibull function from among three candidates as one which provides a reasonable two-parameter fit for most observed SEP events. In addition to the peak intensity, \(I_{\mathrm{p}}\), each event energy range can be described by shape and duration parameters \(\alpha\) and \(\beta\). Fits are applied to the profiles of 14 recent large SEP events observed in three integral energy ranges by the Geostationary Operational Environmental Satellite (GOES) spacecraft. The fits are generally robust, with \({<}\,1\%\) uncertainties in the parameters, but they can be very dependent on the choices of fit end times. We show the fit parameters as functions of energy range and solar source longitude. The fit parameters can be used not only as targets for modeling efforts, but also in space weather applications.