| Solar flares are one of the most energetic events in the solar atmosphere, which last minutes to tens of minutes. The eruption of a solar flare involves energy release, plasma heating, particle acceleration, mass flows, waves, etc.. A solar flare releases a large amount of energy, and its emission spans a wide wavelength range. Solar flares are usually accompanied by coronal mass ejections (CMEs); therefore they could sig-nificantly affect the space environments between the Earth and the Sun.At present, we do not fully understand the whole flare process. There are still many important questions to be resolved, such as when and where is the energy re-leased? What are the main ways of energy release? How long does the energy release last? And how does the solar atmosphere respond to the energy release? To address these questions, we study in detail the flare heating and dynamic evolution. We first give a brief review of previous flare studies (Chapter1), and introduce the observing instruments (Chapter2) and modeling method (Chapter3) related to this thesis work. Then we use spectral data to investigate the chromospheric evaporation (Chapter4). Based on the results, we further explore the flare heating problem. With observation-ally inferred heating functions, we model two flare loops and compare the results with observations (Chapter5). A consistency is achieved between modeling and observa-tions. In addition, we model two different flare loop systems with quite different heating profiles and dynamic evolutions (Chapter6). The details are described as below.Firstly, we investigate the chromospheric evaporation in the flare on2007January16using line profiles observed by the Extreme-ultraviolet (EUV) Imaging Spectrome-ter (EIS) on board Hinode. Three points at flare ribbons of different magnetic polarities are analyzed in detail. We find that the three points show different patterns of upflows and downflows in the impulsive phase of the flare. The spectral lines at the first point are mostly blueshifted, with the hotter lines showing a dominant blueshifted compo-nent over the stationary one. At the second point, however, only weak upflows are detected; instead, notable downflows appear at high temperatures (up to2.5-5.0MK). The third point is similar to the second one except that it shows evidence of multi-component downflows. While the evaporated plasma falling back down as warm rain is a possible cause of the redshifts at the second and third points, the different patterns of chromospheric evaporation at the three points imply the existence of different heating mechanisms in the flaring region.Then, we study the flare heating and dynamics using the "enthalpy-based ther-mal evolution of loops"(EBTEL) model. We analyze an M1.0flare on2011February16. This flare is composed of two distinctive loop systems observed in EUV images. The UV1600A emission at the feet of these loops exhibits a rapid rise, followed by enhanced emission in different EUV channels observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Such a behavior is indicative of impulsive energy deposit and the subsequent response of overlying coro-nal loops. Using the method recently developed, we infer empirical heating functions from the rapid rise of the UV light curves for the two loop systems, respectively, treated as two big loops with cross-sectional area of5" by5", and compute the plasma evolu-tion in the loops using the EBTEL model. We further compute the synthetic EUV light curves, which, with the limitation of the model, agree reasonably with the observed light curves obtained in multiple AIA channels and EIS lines:they show the same evolution trend and their magnitudes are comparable within a factor of two. We also compare the computed mean enthalpy flow velocity with the Doppler shifts of EIS lines during the decay phase of the two loops. Our results suggest that the two different loops with dif-ferent heating functions as inferred from their footpoint UV emission, combined with their different lengths as measured from imaging observations, give rise to different coronal plasma evolution patterns as revealed in both models and observations.With the same method, we further analyze another C4.7flare. From AIA imaging observations, we can identify two sets of loops in this event. EIS spectroscopic obser-vations reveal blueshifts at the feet of both sets of loops during the impulsive phase. However, the dynamic evolutions of the two sets of loops are quite different. The first set of loops exhibits blueshifts (～10km s-1) for about25minutes followed by redshifts, while the second set shows stronger blueshifts (～20km s-) which are maintained for about an hour. The long-lasting blueshifts in the second set of loops are indicative of continuous heating. The UV1600Aobservation by AIA also shows that the feet of the loops brighten twice with15minutes apart. The first set of loops, on the other hand, brighten only once in the U V band. We construct heating functions of the two sets of loops using spatially resolved UV light curves at their footpoints, and model plasma evolution in these loops with the EBTEL model. The results show that, for the first set of loops, the synthetic EUV light curves from the model compare favorably with the observed light curves in six AIA channels and eight EIS spectral lines, and the com-puted mean enthalpy flow velocities also agree with the Doppler shifts measured in EIS lines. For the second set of loops modeled with twice-heating, there are some discrep-ancies between modeled and observed EUV light curves at low-temperature lines, and the model does not fully reproduce the prolonged blueshift signatures as observed. The prominent discrepancies between model and observations for the second set of loops may be caused by non-uniform heating localized especially at the loop footpoints which cannot be modeled by the0D EBTEL model, or by unresolved fine flaring strands in the loops with quite different heating rates and profiles. |
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