Ensemble Numerical Simulations of Realistic SEP Events and the Inspiration for Space Weather Awareness

The solar energetic particle(SEP)event is a kind of hazardous space weather phenomena,so its quantitative forecast is of great importance from the aspect of space environmental situation awareness.We present here a set of SEP forecast tools,which consists of three components:(1)a simple polytropic solar wind model to estimate the background solar wind conditions at the inner boundary of 0.1 AU(about 20 R⊙);(2)an ice-cream-cone model to estimate the erupted coronal mass ejection(CME)parameters;and(3)the improved Particle Acceleration and Transport in the Heliosphere(i PATH)model to calculate particle fluxes and energy spectra.By utilizing the above models,we have simulated six realistic SEP events from 2010 August 14 to 2014 September 10,and compared the simulated results to the Geostationary Operational Environmental Satellites(GOES)spacecraft observations.The results show that the simulated fluxes of>10 Me V particles agree with the observations while the simulated fluxes of>100 Me V particles are higher than the observed data.One of the possible reasons is that we have adopted a simple method in the model to calculate the injection rate of energetic particles.Furthermore,we have conducted the ensemble numerical simulations over these events and investigated the effects of different background solar wind conditions at the inner boundary on SEP events.The results imply that the initial CME density plays an important role in determining the power spectrum,while the effect of varying background solar wind temperature is not significant.Naturally,we have examined the influence of CME initial density on the numerical prediction results for virtual SEP cases with different CME ejection speeds.The result shows that the effect of initial CME density variation is inversely associated with CME speed.