The Relationship between Chirality, Sense of Rotation, and Hemispheric Preference of Solar Eruptive Filaments

Abstract

The orientation, chirality, and dynamics of solar eruptive filaments is a key to understanding the magnetic field of coronal mass ejections (CMEs) and therefore to predicting the geoeffectiveness of CMEs arriving at Earth. However, confusion and contention remain over the relationship between the filament chirality, magnetic helicity, and sense of rotation during eruption. To resolve the ambiguity in observations, in this paper, we used stereoscopic observations to determine the rotation direction of filament apex and the method proposed by Chen et al. (2014) to determine the filament chirality. Our sample of 12 eruptive active-region filaments establishes a strong one-to-one relationship, i.e., during the eruption, sinistral/dextral filaments (located in the southern/northern hemisphere) rotate clockwise/counterclockwise when viewed from above, and corroborates a weak hemispheric preference, i.e., a filament and related sigmoid both exhibit a forward (reverse) S shape in the southern (northern) hemisphere, which suggests that the sigmoidal filament is associated with a low-lying magnetic flux rope with its axis dipped in the middle. As a result of rotation, the projected S shape of a filament is anticipated to be reversed during eruption.

The Rotation of Magnetic Flux Rope Formed during Solar Eruption

“…Meanwhile, during its eruption, the apex part of the filament displays CCW rotation, which can be seen in both SDO and STEREO-A observations (Figure 2(b),(d), and accompanied anima-tion). This event is a well-observed example supporting a strong one-to-one relationship during the eruption as found by Zhou et al (2020); sinistral/dextral filaments rotate clockwise (CW)/counterclockwise (CCW) when viewed from above, and the morphology of the filament and related sigmoid both exhibit a forward (reverse) S shape.…”

“…Indeed, observations of filament eruptions show that there is a one-to-one correlation between the rotation direction and the filament chirality (or sign of helicity of the corresponding mag-netic field); sinistral (dextral) filaments with positive (negative) helicity rotate clockwise (counterclockwise) when viewed from above (Green et al 2007). Furthermore, the pre-eruptive morphology of filaments corroborates an moderate hemispheric preference, namely, filaments of forward (reverse) S shape are usually located in the southern (northern) hemisphere and have a positive (negative) helicity (Rust & Kumar 1996;Zhou et al 2020). Besides, there are coronal loops presenting S shape known as sigmoids observed in extreme ultraviolet (EUV) and soft X-ray (SXR) passbands (Cheng et al 2017), and in many events the sigmoid is found to be co-spatial roughly with the pre-eruptive filament.…”

“…The footpoints of the magnetic field supporting the filament can be located by where the filament plasma flows down to the solar surface. The observed right-skewed drainage sites relative to the PIL implies that the filament chirality is dextral (Chen et al 2014;Zhou et al 2020). Meanwhile, during its eruption, the apex part of the filament displays CCW rotation, which can be seen in both SDO and STEREO-A observations (Figure 2(b),(d), and accompanied anima-tion).…”

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

“…Alternatively, Chen et al (2014) proposed that a filament is dextral (sinistral) if during the eruption the conjugate sites of plasma draining are right-skewed (left-skewed) with respect to the PIL. Employing this new criteria, it is found that the hemispheric rule of filament chirality is significantly strengthened (Ouyang et al 2017;Zhou et al 2020b).…”

Some interesting topics provoked by the solar filament research in the past decade

“…However, 2D images might cheat our eyes as demonstrated by a famous animation picture, where a dancing girl can be recognized to rotate clockwise or counterclockwise. In this sense, 3D construction of the filament shapes and motions based on stereoscopic or spectroscopic observations are important (Li et al 2010b(Li et al , 2011Song et al 2018;Zhou et al 2020b). -Allowance height: Observations indicated that most prominences have an upper edge below 50 Mm, and the maximum height of the upper edge of quiescent prominences is ∼500 Mm (Wang et al 2010).…”