Research In Ensemble Prediction Of The Solar Energetic Particle Event

A very important aspect of the space environment situation awareness is to forecast the solar energetic particle(SEP)events quantitatively.Generally,high energy particles in most of the major SEP events originate in the front area of coronal mass ejection(CME)-driven shocks and are accelerated by diffusive shock acceleration(DSA)mechanism.Many of the theoretical work and forecast model and technique development appear in the literature in the last two decades.In this paper,we present an SEP forecast tool set,which consists of three components: 1)a simple polytropic solar wind model to estimate the background solar wind conditions at the inner boundary of 0.1AU(～20 solar radii);2)an ice-cream-cone model to estimate the erupted CME parameters;3)the improved Particle Acceleration and Transport in the Heliosphere(i PATH)model to calculate particle flux and energy spectrum.Utilizing the above tool set,we numerically simulate a series of realistic SEP events,and perform ensemble simulations for several crucial inner-boundary parameters.In this paper,we have simulated a realistic solar energetic particle(SEP)event on09/30/2013 and compared the results to the GOES spacecraft observations.The results show that the simulated flux of ≥10Me V particles fits the observation well while the simulated flux of ≥ 100 Me V particles is a little higher than the observed result.Furthermore,we have conducted the ensemble numerical simulations over the particular event and investigated the effects of different CME speeds as well as the background solar wind temperatures at the inner-boundary on SEP events.The results imply that CME speeds play a very important role in determining the particle flux and power spectrum while the effect of varying background solar wind temperature is negligible.Beyond the single-event study,the ensemble simulation for multiple realistic SEP events is further carried out in this paper.We have simulated six realistic SEP events from 2010 August 14 to 2014 September 10,and quantitatively analyze the disagreements between our simulations and the GOES observations.The results support the previous study of the single-event.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: 1)the initial CME density plays an important role in determining the power spectrum;2)the effect of varying background solar wind temperature is not significant(which supports the conclusion of the single-event study).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.