Horizontal photospheric flows trigger a filament eruption

Abstract

Context. A large filament composed principally of two sections erupted sequentially in the southern hemisphere on January 26 2016. The central, thick part of the northern section was first lifted up and lead to the eruption of the full filament. This event was observed in Hα with the Global Oscillation Network Group (GONG) and Christian Latouche IMageur Solaire (CLIMSO), and in ultraviolet (UV) with the Atmospheric Imaging Assembly (AIA) imager on board the Solar Dynamic Observatory (SDO). Aims. The aim of the paper is to relate the photospheric motions below the filament and its environment to the eruption of the filament.Methods. An analysis of the photospheric motions using Solar Dynamic Observatory Helioseismic and Magnetic Imager (SDO/HMI) continuum images with the new version of the coherent structure tracking (CST) algorithm developed to track granules, as well as large-scale photospheric flows, has been performed. Following velocity vectors, corks migrate towards converging areas.Results. The supergranule pattern is clearly visible outside the filament channel but difficult to detect inside because the modulus of the vector velocity is reduced in the filament channel, mainly in the magnetized areas. The horizontal photospheric flows are strong on the west side of the filament channel and oriented towards the filament. The ends of the filament sections are found in areas of concentration of corks. Whirled flows are found locally around the feet. Conclusions. The strong horizontal flows with an opposite direction to the differential rotation create strong shear and convergence along the magnetic polarity inversion line (PIL) in the filament channel. The filament has been destabilized by the converging flows, which initiate an ascent of the middle section of the filament until the filament reaches the critical height of the torus instability inducing, consequently, the eruption. The n decay index indicated an altitude of 60 Mm for the critical height. It is conjectured that the convergence along the PIL is due to the large-scale size cells of convection that transport the magnetic field to their borders.

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

“…A detailed investigation and confirmation of our scenario is not possible without proper MHD modelling, which is beyond scope of this paper. Our findings are consistent with those of Roudier et al (2018), who concluded that the filament destabilisation was caused by the joined action of the differential rotation shear and convergent flows towards the filament.…”

Solar surveillance with CLIMSO: instrumentation, database and on-going developments

“…L1 is used to image the full disk of the sun (top left panel of Fig. 3) and essentially to capture and watch the evolution of filaments (Roudier et al, 2018). L1's resulting effective focal length is 1350 mm.…”

Difference of source regions between fast and slow coronal mass ejections

“…Some filament material falls to the filament ends and to an intermediate footpoint. Roudier et al (2018) studied triggers of this filament eruption. They concluded that the filament was destabilized by converging photospheric flows below it, which initiated an ascent of the middle section of the filament up to the critical height of the torus instability.…”