Studies Of The Transport Effect Of Energetic Particles In The Magnetic Cloud And Sheath Region And The Prediction Of The Sunspot Number

Solar energetic particles（SEPs）and galactic cosmic rays（GCRs）are important sources of particle radiation in the space,which pose serious threats to space activities and human life,so that it is necessary to evaluate the radiation hazards of energetic particles on the scale of minutes to decades.On the short-term scale,it is necessary to solve the problem of how to predict the flux of energetic particles accurately in a solar event,so as to provide data for evaluating the radiation hazards of energetic particles.On the long-term scale,because SEPs and GCRs are positively and inversely correlated with the level of solar activity,it is necessary to solve the problem of how to predict the evolution of solar activity decades in advance.Traditionally,the numerical simulation of the transport effect of energetic particles adopts a simple Parker field,and there are usually some large-scale structures with non-Parker field in the interplanetary space.Therefore,this dissertation studies the transport effect of energetic particles in the two large-scale interplanetary structures of magnetic cloud and sheath,which is of great significance to predict the flux of energetic particles accurately in a solar event.Sunspot number（SSN）is a good indicator of solar activity.Therefore,this dissertation studies the long-term prediction of SSN,which is of great significance to evaluate the flux of energetic particles on the long-term scale.In a ground-level enhancement event（GLE59）of SEPs,it is observed that the flux of energetic particles showed a two-step decrease structure due to the depression of magnetic cloud and sheath,of which the characteristics are reproduced by the numerical simulation.The research shows that the magnetic cloud–sheath structure has little effect on the proton intensity observed by the observer before the shock arriving at the observer,but it can inhibit the proton intensity significantly after the shock passing through the observer,and the first-step decrease is greater than the second-step one.The depression lasts for about 2 days,so that it is a local effect of flux inhibition.The research also shows that the variation of magnetic field turbulence level and the enhancement of magnetic field strength can not produce the two-step decrease alone,and the combination of turbulence level and magnetic field strength has a greater effect on the depression of SEP intensity than simply superimposing them.The simulation results with only magnetic cloud or sheath show that the sheath contributes most of the decrease,and the magnetic cloud plays an important role in the formation of the second-step decrease.We have reproduced the two-step Forbush decrease（FD）,caused by the magnetic cloud and sheath,in GCR intensities accompanied by the GLE59 event by numerically solving the focusing transport equation.In general,the simulation results with the mag-netic cloud–sheath included reproduce the main characteristics of the observation,such as the pre-increase precursor,two-step decrease,amplitude,and total recovery time.The two-step decrease occurs when the magnetic cloud and sheath arrived at the observer.The simulation results with only magnetic cloud or sheath included show that the FD amplitude caused by the sheath is large but the recovery time is short,while the FD amplitude caused by the magnetic cloud is small but the recovery time is long.Therefore,the sheath plays an important role in the amplitude of the two-step decrease FD,while the magnetic cloud contributes to the formation of the second-step decrease and prolongs the recovery time of FD.The simulation also shows that the magnetic field turbulence level and background magnetic field strength in the magnetic cloud–sheath are crucial for the formation of the two-step FD associated with the GLE59 event,indicating that when there are large-scale interplanetary structures,the effects of the drastic change of turbulence level and the enhancement of magnetic field strength need to be considered in the GCR simulation,so that it is necessary to use the focused transport equation instead of the Parker equation.We have constructed an SSN model to describe the evolution of solar cycles according to the modified logistic function,and based on the SSN model we have proposed the SSN prediction models TMLP and TMLP-E,which can predict the evolution of SSN with time about one and two solar cycles in advance,respectively.The confidence intervals of the solar cycle amplitude₈),ascent time₍（6）,and cycle length_{（8）predicted by the TMLP model at the 95%significant level are[-22.7%,18.4%],[-34.6%,38.8%],and[-24.3%,17.7%],respectively.The confidence intervals of8},₍（6）,and₍（8）predicted by the TMLP-E model are[-41.9%,33.9%],[-43.1%,62.5%],and[-28.9%,22.8%],respectively.The predictions of SSN at solar cycles 25 and 26 are made by using the TMLP and TMLP-E models.The predicted amplitude of solar cycle 25 is 115.1,and the confidence interval is[101.8,136.3];The peak time will occur in October 2024,and the confidence interval is[February 2023,September 2026];Solar cycle 25 is expected to end in January2031,and the confidence interval is[May 2028,December 2032].The predicted amplitude of solar cycle 26 is 107.3,and the confidence interval is[62.3,143.6];The peak time will occur in November 2035,and the confidence interval is[October 2033,November2038];Solar cycle 26 is expected to end in January 2041,and the confidence interval is[November 2038,July 2044].The prediction results show that the solar activity levels of solar cycles 25 and 26 will be similar to that of solar cycle 24,i.e.,they are at a relatively low level.Therefore,solar cycles 24–26 will form a new minimum of the Gleissberg cycle.