Formation and Eruption of a Mini-sigmoid Originating in Coronal Hole

Abstract

In this paper, we study in detail the evolution of a mini-sigmiod originating in a cross-equatorial coronal hole, where the magnetic field is mostly open and seriously distinct from the closed background field above active-region sigmoids. The source region first appeared as a bipole, which subsequently experienced a rapid emergence followed by a long-term decay. Correspondingly, the coronal structure initially appeared as arc-like loops, then gradually sheared and transformed into continuously sigmoidal loops, mainly owing to flux cancellation near the polarity inversion line. The temperature of J-shaped and sigmoidal loops is estimated to be about 2.0 × 10 6 K, greater than that of the background coronal hole. Using the flux-rope insertion method, we further reconstruct the nonlinear force-free fields that well reproduces the transformation of the potential field into a sigmoidal field. The fact that the sheared and sigmoidal loops are mainly concentrated at around the high-Q region implies that the reconnection most likely takes place there to form the sigmoidal field and heat the plasma. Moreover, the twist of sigmoidal field lines is estimated to be around 0.8, less than the values derived for the sigmoids from active regions. However, the sigmoidal flux may quickly enter an unstable regime at the very low corona (< 10 M m) due to the open background field. The results suggest that the mini-sigmoid, at least the one in our study, has the same formation and eruption process as the large-scale one, but is significantly influenced by the overlying flux.

High-resolution Observation and Magnetic Modeling of a Solar Minifilament: The Formation, Eruption, and Failing Mechanisms

“…This method has been successfully applied to model the source regions of large-scale events such as active region filaments (Bobra et al 2008;Su et al 2009aSu et al , 2009bSu et al , 2011Su et al , 2018, quiescent filaments (Su & van Ballegooijen 2012;Su et al 2015), a double-decker filament (Chen et al 2021), sigmoids (Savcheva & van Ballegooijen 2009;Savcheva et al 2012), an erupting pseudostreamer (Karna et al 2021), a blowout jet (Farid et al 2022), and so on. The smallest structure we have modeled so far is a minisigmoid with ∼20″ in length (Huang et al 2019).…”

Growth of a filament channel by intermittent small-scale magnetic reconnection

“…Coronal mass ejections (CMEs) are large-scale explosive phenomena in the solar system that can give rise to severe space weather events (Chen 2011). A promising method to forecast the occurrence of CMEs is to monitor their pre-eruptive configurations, including filaments, coronal cavities, sigmoids, and hot channels (Low & Hundhausen 1995;Hudson & Lemen 1998;Wang & Stenborg 2010;Zhang et al 2012;Cheng et al 2013Cheng et al , 2014Huang et al 2019). These pre-eruptive structures can be regarded as different manifestations of a common configuration, namely the so-called filament channels (FCs), at different evolutionary stages and/or in different plasma environments as suggested by a recent review paper by Patsourakos et al (2020).…”

Grow-up of a Filament Channel by Intermittent Small-scale Magnetic Reconnection

“…Coronal mass ejections (CMEs) are large-scale explosive phenomena in the solar system and can give rise to severe space weather events (Chen 2011). A promising method to forecast the occurence of CMEs is to monitor their pre-eruptive configurations including filaments, coronal cavities, sigmoids, and hot channels (Low & Hundhausen 1995;Hudson et al 1998;Wang & Stenborg 2010;Zhang et al 2012;Cheng et al 2013Cheng et al , 2014Huang et al 2019). In a sense, these pre-eruptive structures can be regarded as different manifestations of a common configuration, i.e., so-called filament channel (FC), at the different evolution stages and/or plasma environments as suggested by a recent review paper by Patsourakos et al (2020).…”