Winking filaments due to cyclic evaporation-condensation

Abstract

Context. Observations have shown that some filaments appear and disappear in the Hα line wing images periodically. There have been no attempts to model these “winking filaments” thus far. Aims. The evaporation-condensation mechanism is widely used to explain the formation of solar filaments. Here, we demonstrate, for the first time, how multi-dimensional evaporation-condensation in an arcade setup invariably causes a stretching of the magnetic topology. We aim to check whether this magnetic stretching during cyclic evaporation-condensation could reproduce a winking filament. Methods. We used our open-source code MPI-AMRVAC to carry out 2D magnetohydrodynamic simulations based on a quadrupolar configuration. A periodic localized heating, which modulates the evaporation-condensation process, was imposed before, during, and after the formation of the filament. Synthetic Hα and 304 Å images were produced to compare the results with observations. Results. For the first time, we noticed the winking filament phenomenon in a simulation of the formation of on-disk solar filaments, which was in good agreement with observations. Typically, the period of the winking is different from the period of the impulsive heating. A forced oscillator model explains this difference and fits the results well. A parameter survey is also done to look into details of the magnetic stretching phenomenon. We found that the stronger the heating or the higher the layer where the heating occurs, the more significant the winking effect appears.