Numerical Simulations On The Formation Of Solar Prominences

Solar prominences are fascinating large-scale, cool (～8000K) and dense (1010-1011cm-3) structures, suspended in the hot and tenuous corona above magnetic neu-tral lines, which separate photospheric magnetic regions with opposite polarity. They are sometimes anchored in the chromosphere by barbs. They are dark features, called filaments, when observed on the solar disk. The physical mechanisms which operate in the formation, maintenance, and instabilities of prominences are complex, involving nonlinear interactions between radiation, conduction, heating, magnetic field reconnec-tion, and gravity, which make these beautiful features of the Sun both fascinating and difficult to study. In this thesis, we focus on the formation of prominences with the aid of numerical simulations.It has been established that cold plasma condensations can form in a magnetic loop subject to localized heating of the footpoints. We perform grid-adaptive numerical sim-ulations of the radiative hydrodynamic equations to investigate the filament formation process in a prescribed loop with both steady and finite-time chromospheric heating. Compared to previous works, we consider low-lying loops with shallow dips, and use a more realistic formula for the radiative loss. We demonstrate for the first time that the onset of thermal instability satisfies the linear instability criterion. The onset time of the condensation is roughly～2hrs or more after the localized heating at the footpoint is effective, and the growth rate of the thread length varies from800km hr-1to4000km hr-1, depending on the amplitude and the decay length scale characterizing this local-ized chromospheric heating. We show how single or multiple condensation segments may form in the coronal portion. In the asymmetric heating case, when two segments form, they approach and coalesce, and the coalesced condensation later drains down into the chromosphere. With a steady heating, this process repeats with a periodicity of several hours. While our parametric survey confirms and augments earlier findings, we also point out that steady heating is not necessary to sustain the condensation. Once the condensation is formed, it keeps growing even after the localized heating ceases. In such a finite-heating case, the condensation instability is maintained by chromospheric plasma which gets continuously siphoned into the filament thread due to the reduced gas pressure in the corona. Finally, we show that the condensation can survive continuous buffeting of perturbations from the photosphericp-mode waves.In the second part, starting from a realistically sheared magnetic arcade connect-ing the chromosphere, the transition region, and the corona, we simulate the in-situ formation and sustained growth of a quiescent prominence in the solar corona. Con-trary to previous works, our model captures all phases of the prominence formation, including the loss of thermal equilibrium, its successive growth in height and width to macroscopic dimensions, and the gradual bending of the arched loops into dipped loops as a result of the mass accumulation. Our2.5-dimensional, fully thermodynamically and magnetohydrodynamically self-consistent model mimics the magnetic topology of normal-polarity prominences above a photospheric neutral line, and results in a curtain-like prominence above the neutral line through which the ultimately dipped magnetic field lines protrude at a finite angle. The prominence formation results from the con-centrated heating in the chromosphere, followed by plasma evaporation and later rapid condensation in the corona due to thermal instability, as verified by linear instabil-ity criteria. Concentrated heating in the lower atmosphere evaporates plasmas from below to accumulate at the top of coronal loops and supply mass to the later promi-nence constantly. This is the first evaporation-condensation model study where we can demonstrate how the formed prominence stays in a force balanced state, which can be compared to the Kippenhahn-Schliiter type magnetohydrostatic model, all in a finite low-beta corona.Finally, the thesis presents the future perspectives of the researches on prominence formation in both observations and simulations.