Abstract
Abstract Combining the Solar Dynamics Observatory and the New Vacuum Solar Telescope observations, we study a confined flare triggered by a rising flux rope within the trailing sunspots of active region 12733. The flux rope lying above the sheared polarity inversion line can be constructed through magnetic extrapolation but could not be detected in multiwavelength images at the pre-flare stage. The conspicuous shearing motions between the opposite-polarity fields in the photosphere are considered to be responsible for the flux rope formation. The maximum twist of the flux rope is as high as −1.76, and then the flux rope rises due to the kink instability. Only when the flare starts can the flux rope be observed in high-temperature wavelengths. The differential emission measure results confirm that this flux rope is a high-temperature structure. Associated with the rising flux rope, there appear many post-flare loops and a pair of flare ribbons. When the rising flux rope meets and reconnects with the large-scale overlying field lines, a set of large-scale twisted loops are formed, and two flare ribbons propagating in opposite directions appear on the outskirts of the former ribbons, indicating that the twist of the flux rope is transferred to a much larger system. These results imply that the external reconnection between the rising flux rope and the large-scale overlying loops plays an important role in the confined flare formation.
Highlights
Solar flares as one of the most energetic phenomena on the Sun have been extensively studied for many years (e.g., Priest & Forbes 2002; Janvier et al 2015; Tian et al 2014; Yang et al 2017), and magnetic reconnection is deemed to be an efficient way for the sudden energy release (Zweibel & Yamada 2009; Yang et al 2015; Wyper et al 2017)
Combining the Atmospheric Imaging Assembly (AIA), Helioseismic and Magnetic Imager (HMI), and New Vacuum Solar Telescope (NVST) observations, we studied a C5.0 confined flare which occurred in active region (AR) 12733 on 26 January 2019
The flare was triggered by a rising magnetic flux rope within the trailing sunspots
Summary
Solar flares as one of the most energetic phenomena on the Sun have been extensively studied for many years (e.g., Priest & Forbes 2002; Janvier et al 2015; Tian et al 2014; Yang et al 2017), and magnetic reconnection is deemed to be an efficient way for the sudden energy release (Zweibel & Yamada 2009; Yang et al 2015; Wyper et al 2017). Magnetic flux ropes appearing as filaments if filled with dark chromospheric material are thought to play a crucial role in the initiation of solar flares. Magnetic reconnection takes place and free energy is released, forming a solar flare (Masuda et al 1994). As revealed by observations and simulations, the strong overlying magnetic loops forming a confining cage can prevent the outward escape of flux ropes, and result in confined flares. We report the observations of a rising flux rope with a two-step evolution process involved in a confined flare, and propose that the external reconnection between the rising flux rope and a part of overlying field lines plays an important role in the confined flare formation
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