Evolution of photospheric flows under an erupting filament in the quiet-Sun region

Abstract

Context. We studied the dynamics of the solar atmosphere in the region of a large quiet-Sun filament, which erupted on 21 October 2010. The filament eruption started at its northern end and disappeared from the Hα line-core filtergrams line within a few hours. The very fast motions of the northern leg were recorded in ultraviolet light by the Atmospheric Imaging Assembly (AIA) imager. Aims. We aim to study a wide range of available datasets describing the dynamics of the solar atmosphere for five days around the filament eruption. This interval covers three days of the filament evolution, one day before the filament growth and one day after the eruption. We search for possible triggers that lead to the eruption of the filament. Methods. The surface velocity field in the region of the filament were measured by means of time-distance helioseismology and coherent structure tracking. The apparent velocities in the higher atmosphere were estimated by tracking the features in the 30.4 nm AIA observations. To capture the evolution of the magnetic field, we extrapolated the photospheric line-of-sight magnetograms and also computed the decay index of the magnetic field. Results. We found that photospheric velocity fields showed some peculiarities. Before the filament activation, we observed a temporal increase of the converging flows towards the filament's spine. In addition, the mean squared velocity increased temporarily before the activation and peaked just before it, followed by a steep decrease. We further see an increase in the average shear of the zonal flow component in the filament's region, followed by a steep decrease. The photospheric line-of-sight magnetic field shows a persistent increase of induction eastward from the filament spine. The decay index of the magnetic field at heights around 10 Mm shows a value larger than critical one at the connecting point of the northern filament end. The value of the decay index increases monotonically there until the filament activation. Then, it decreased sharply.

The Evolution of Photospheric Magnetic Fields at the Footpoints of Reconnected Structures in the Solar Atmosphere

“…Meanwhile, the fields become nonpotential and energetic (Shimizu et al 2014). As revealed in previous studies, highly twisted (Rust & Kumar 1996;Titov & Démoulin 1999) or sheared (Bobra et al 2008;Roudier et al 2008;Wollmann et al 2020) magnetic flux rope typically suggests strong complexity and nonpotentiality, as well as more free magnetic energy of the fields (Yamada et al 2010). In this study, the sigmoid-like structure (Rust & Kumar 1996) in Figure 4 magnetic reconnection may be triggered easily in a nonpotential environment.…”

“…As a result of the horizontal flows, Roudier et al (2008) have revealed an increase in the shear below the point where the filament eruption starts and a decrease in shear after the eruption, and they conclude that the shear pumps the energy to the atmospheric structure. Largescale flows in the direction opposite to the differential rotation can create strong shear along the magnetic polarity inversion line of a filament channel, which influences the stability of the structure and contributes to the eruption of the filament (Roudier et al 2018;Wollmann et al 2020).…”

Texture of average solar photospheric flows and the donut-like pattern

“…For example, the convection cells transport the magnetic field and form a magnetic polarity inversion line between them (Roudier et al 2018a). A previous study shows the importance of the photospheric flows for influencing the stability of the structures of the magnetic field in upper layers of the solar atmosphere (Wollmann et al 2020), for example in the destabilation and eruption of solar filaments.…”