Radiative Hydrodynamic Simulations Of The Solar White-Light Flares

Solar white-light flares(WLFs)are relatively special among all the recorded solar flares.WLFs are one kind of solar flares characterized by an enhancement in the whole optical continuum.It is generally acknowledged that solar flares are one of the most vio-lent solar activities,which release a great amount of energy in a short period and play an important role in human daily life and space activities.In general,WLFs are regarded to be the most violent and energetic flare events.Therefore,the study of WLFs is closely related to our present and future life.At the same time,studying WLFs itself can show great significance in science.There are still many problems and controversies in the interpretation of the observed WLFs by the existing flare models.As a special kind of solar flare,studying WLFs may reveal the common and special aspects of solar flares.In recent years,with the development of observational technology and instruments,the observational data of WLFs,especially the spectral data,has been continuously accu-mulated,which greatly promotes the research process of WLFs.However,due to its particularity and the limitation of observational methods and conditions,it is far from enough to study WLFs by observation alone.As a result,the research method of nu-merical simulation has become a powerful complement to the observational research method.The main purpose of this paper is to study the response of the flaring atmosphere to heating(non-thermal-electron beam)through radiative hydrodynamic simulation pro-gram RADYN to calculate some spectral lines as well as the continuum emission at some wavelengths during WLFs.The main contents of this thesis are as follows:In Chapter 1,we briefly introduce the basic knowledge of solar flares,especially WLFs.We give a brief introduction to the research background and significance on WLFs,especially the previous studies using numerical methods to study WLFs.At the same time,the spectral characteristics of WLFs and the spectral lines used in our study are also mentioned.In Chapter 2,we present the concept of radiative hydrodynamic simulations.The calculation program RADYN is briefly described.And the spectral line calculation pro-gram RH which features calculations under the PRD(partial frequency redistribution)assumption is also introduced.We also discuss the parameter configuration in our sim-ulation in this chapter.In Chapter 3,We take non-thermal electron beams as the energy source for the WLFs in two different initial atmospheres and vary the electron beam parameters,and totally that we have 20 different sets of parameter combinations.By conducting radiative hydrodynamics simulations,we investigate the response of the continuum at 3600 A and 4250 A and also the hydrogen H? and Ly? lines during WLFs.Our results show that the model with non-thermal electron beam heating can clearly show enhancements in all studied wavelengths.The electron beam can also influence the Balmer jump effectively.A larger electron beam flux causes a greater emission enhancement.And a smaller spectral index or a penumbral initial atmosphere leads to a stronger emission increase at 3600 A,4250 A,and in the Ha line.For the Lya line,however,it is more preferably enhanced in a quiet-Sun initial atmosphere with a larger spectral index of the electron beam.It is also notable that the continua at 3600 A and 4250 A and the Ha line exhibit a dimming at the beginning of the heating and reach their peak emissions later than the peak time of the heating function,while the Lya line does not show such behaviors.In the end,we summarize our simulation work and describe the innovation and possible improvement for future research in Chapter 4.