Finding the Critical Decay Index in Solar Prominence Eruptions

Abstract

The background field is assumed to play prime role in the erupting structures like prominences. In the flux rope models, the critical decay index (n c ) is a measure of the rate at which background field intensity decreases with height over the flux rope or erupting structure. In the real observations, the critical height of the background field is unknown, so a typical value of n c = 1.5 is adopted from the numerical studies. In this study, we determined the n c of 10 prominence eruptions (PEs). The prominence height in 3D is derived from two-perspective observations of Solar Dynamics Observatory and Solar TErrestrial RElations Observatory. Synoptic maps of photospheric radial magnetic field are used to construct the background field in the corona. During the eruption, the height-time curve of the sample events exhibits the slow and fast-rise phases and is fitted with the linear-cum-exponential model. From this model, the onset height of fast-rise motion is determined and is considered as the critical height for the onset of the torus-instability because the erupting structure is allowed to expand exponentially provided there is no strapping background field. Corresponding to the critical height, the n c values of our sample events are varied to be in the range of 0.8-1.3. Additionally, the kinematic analysis suggests that the acceleration of PEs associated with flares are significantly enhanced compared to flare-less PEs. We found that the flare magnetic reconnection is the dominant contributor than the torus-instability to the acceleration process during the fast-rise phase of flareassociated PEs in low corona (< 1.3R ).

Critical decay index for eruptions of ‘short’ filaments

“…(2019). Low values of the decay index at the height from which prominences start eruption were reported by Lee et al (2016), Vasantharaju et al (2019), Rees-Crockford et al (2020), Filippov (2020.…”

Magnetic Flux Ropes in the Solar Corona: Structure and Evolution toward Eruption

“…In a data-driven MHD simulation, Guo et al (2019a) computed the decay index along the eruption path of a flux rope, and found that the rope starts to rise rapidly at the same height as the decay index crosses the canonical critical value of 1.5. Similarly, recent studies on the height-time profiles of eruptive filaments (Vasantharaju et al 2019;Zou et al 2019b;Myshyakov & Tsvetkov 2020;Cheng et al 2020) and of hot channels (Cheng et al 2020) generally concluded that the decay index at the height where the slow rise transitions to fast rise is close to the threshold of the torus instability.…”

Prominence instability and CMEs triggered by massive coronal rain in the solar atmosphere

“…But the ini-tial rise of prominence seems to be caused by coronal rain, which presumably is the result of thermal instability. Vasantharaju et al (2019) suggested that the slow rise phase can be connected with the ideal kink instability of flux rope. Let us examine this possibility for the event of May 16-18, 2011.…”

“…Most acceptable triggering mechanism for the prominence instability is connected to twisted magnetic config-urations. It has been observed that the kink instability of magnetic flux ropes (Williams et al 2005), the torus instability (Filippov 2013, Zuccarello et al 2014 or both together (Vasantharaju et al 2019) can lead to CME initiations.…”