The Research About Mean Free Path Of Solar Energetic Particles In Three-dimensional MHD Background

Space physics is a discipline that has emerged rapidly after lots of satellites which were send into space.As a part of space physics,space weather,especially space disaster events,has an extremely important impact on human production and life.Solar Energetic Particle(SEP)is considered to be one of the most important disaster events,which can cause damage to spacecraft,threaten the life of astronauts,and even cause communication failure and navigation failure,which affects human economic activities and life.Therefore,how to accurately predict SEP has always been one of the important topics in space weather research.Currently,for the transmission process of SEP,the transmission model usually used a constant solar wind speed or a Parker spiral magnetic field.The advantage is that can effectively simplify the forecasting process and improve the timeliness of forecasting.However,with the increasing demand for prediction accuracy and computer computing development,it is more important to simulate based on the real heliosphere as the transmission background.In this paper,the MHD-SEP model of the solar wind background field obtained by three-dimensional MHD simulation is used to simulate the SEP transmission.The background field of the model can reflect the main physical phenomena in the interplanetary background solar wind,such as the interaction between Coronal hole high speed stream and Coronal hole low speed stream in 1AU.The forward shock and the backward shock,the interaction of shocks and the three-dimensional structure of the heliospheric current sheet are not reflected by the traditional models.This paper we makes full use of the advantages of this model with the three-dimensional solar wind background.The main work is as follows:(1)Using different models for the mean free path,and analyzing the optimal the mean free path model in the mode(2)In this mode,the sensitivity of the relevant free parameters affecting the mean free path was tested.(3)Qualitative analysis of the mean free path of solar energetic particles in high and low solar activity.We use this model to obtain the spatial distribution of the mean free path consistent with the predecessors.On this basis,the conclusions are obtained:(1)The different mean free path solution models in the MHD background have a significant influence for omnidirectional flux of SEP,so it is necessary to select a model suitable for the model.The model we use more consistent with actual observations.(2)The relevant free parameters of the mean free path have a great influence on the omnidirectional flux value in the MHD background.But for particles’ anisotropy is not significant.The model can satisfy the qualitative analysis.And this work make the foundation for quantitative analysis in future work.(3)The spatial distribution of parallel mean free path in different events can be reflected in this mode.It is used as an important reference for the study of SEP.(4)The mean free path has a significant negative correlation with the radial velocity of the solar wind.This conclusion links SEP with the background solar wind and also provides a basis for the study of SEP’ transport in the background solar wind with more complex CME.