Numerical Experiments On Physical Properties Of The Current Sheet In The Solar Two-ribbon Flare

Large scale current sheets are important structures in solar eruptions. Mod-els of coronal mass ejection (CME)/fare include the large scale current sheetconnecting the ejected fux rope to the post-fare loop. Studies of physical prop-erties in current sheets could improve our understanding on rapid magnetic re-connection during a solar eruption, instabilities and turbulence and high-energyparticle acceleration taking place inside the current sheet. This thesis focuseson the physical properties, internal structures, and the features of emission linesof current sheets that form during solar eruptions by performing numerical ex-periments, and giving predictions from CME/fare models to be compared withobservations.We perform resistive magnetohydrodynamic simulations to study the inter-nal structure of current sheets that form during solar eruptions. The simulationsstart with a vertical current sheet in mechanical and thermal equilibria, whichseparates two regions of the magnetic felds of opposite polarity that are line-tiedto the lower boundary representing the photosphere. Reconnection commencesgradually due to an initially perturbation to the system, but becomes fasterwhen plasmoids appear and produce small-scale structures inside the currentsheet. These structures include magnetic islands or plasma blobs fowing in bothdirections along the sheet, and X-points between pairs of adjacent islands. Weshow detailed evolutions of the current sheet and look into dynamical featuresof magnetic islands or plasmoids. Then we examine the statistical properties ofthe fne structure and the dependence of the energy spectra on these properties.The spectral profles of magnetic and kinetic energy inside the current sheet areboth of the power law. The corresponding spectral indices are found to varywith the magnetic Reynolds number Rmof the system, but tend to approachto a constant for large (R5m>10). The motion and growth of blobs changethe spectral index. The growth of new islands causes the power spectrum tosteepen, but spectrum becomes shallower when old and large plasmoids leave the computational domain.To understand observational features and physical properties of CME/farecurrent sheets, we deduced some important results and the corresponding obser-vational consequences from fare/CME models in order to compare with obser-vations, such as those from Atmospheric Imaging Assembly (AIA) on the SolarDynamics Observatory and Ultraviolet Coronagraph Spectrometer on the Solarand Heliospheric Observatory. We used a simulation of a large-scale CME cur-rent sheet previously reported by Reeves et al., and performed time-dependentionization calculations of the plasma fow in a CME/fare current sheet. Theresults show diferences in the emission line intensities between equilibrium andnon-equilibrium ionizations. The current sheet plasma is found under-ionizedat low altitude and over-ionized at high altitude. The assumption of ionizationequilibrium would lead to a signifcant underestimate of the temperature low inthe current sheet and overestimate at larger heights. By assuming intensities ofemission line, we compute the count rates for each of the AIA bands and emissionfeatures, and compare the results with observations from UVCS, including a lowintensity region around the current sheet corresponding to this model.