We discuss the formation mechanism of a solar prominence by in-situ radiative condensation using MHD simulations including optically thin radiative cooling and thermal conduction.
The radiative condensation, or thermal nonequilibrium, is considered to be a key process for prominence formation. In the previous theoretical studies, the radiative condensation is triggered chromospheric evaporation, namely, the thermal imbalance in the coronal loop is created by the injection of the dense plasmas from the chromosphere. On the other hand, a recent observational study could not find the evidence of chromospheric evaporation in the radiative condensation event, and claimed that it was in-situ condensation.
Motivated by these facts, we propose a model of in-situ radiative condensation and demonstrate it by MHD simulation including optically thin radiative cooling and thermal conduction. In our model, the flux rope is formed by the reconnection at the footpoint of the coronal arcade field where the conversing and shearing motions are imposed. The thermal imbalance is created inside the flux rope due to the relatively dense coronal plasma. The thermal conduction along the closed magnetic field does not suppress the thermal imbalance, leading to the radiative condensation. Our numerical simulations succeeded in reproducing the prominence through this process. The time evolution of synthesized multi-wavelength EUV emissions shows the temporal and vertical shift, which is consistent with the observation. The synthesized differential emission measure also agrees with observation. Moreover, we find the power-law relationship between temperature and density along each magnetic field line in the prominence-coronal cavity transition. There is a possibility that the power-law is found in multi-wavelength EUV observations of coronal cavity by Hinode/EIS.