How Many Twists Do Solar Coronal Jets Release?

Abstract

Highly twisted magnetic flux ropes, with finite length, are subject to kink instabilities, and could lead to a number of eruptive phenomena in the solar atmosphere, including flares, coronal mass ejections (CMEs) and coronal jets. The kink instability threshold, which is the maximum twist a kink-stable magnetic flux rope could contain, has been widely studied in analytical models and numerical simulations, but still needs to be examined by observations. In this article, we will study twists released by 30 off-limb rotational solar coronal jets, and compare the observational findings with theoretical kink instability thresholds. We have found that: 1) the number of events with more twist release becomes less; 2) each of the studied jets has released a twist number of at least 1.3 turns (a twist angle of 2.6π); and 3) the size of a jet is highly related to its twist pitch instead of twist number. Our results suggest that the kink instability threshold in the solar atmosphere should not be a constant. The found lower limit of twist number of 1.3 turns should be merely a necessary but not a sufficient condition for a finite solar magnetic flux rope to become kink unstable.

Observation and modelling of solar jets

“…Specifically, the statistical studies carried out by Moore et al [64,186] found the existence of obvious axial rotation in both standard and blowout jets; their results showed that the number of turns of axial rotation ranged from 0.25 to 2.5. Other case studies showed that the number of turns of axial rotation ranged from about 0.34 to 4.7 [187–190], and the periods were measured to be 1–20 min [174,191,192].…”

Magnetic Twists of Solar Filaments

“…With respect to the kink instability, the widely adopted critical value was proposed by Hood & Priest (1981), where they considered a line-tying, force-free, uniform twisted flux rope and found that an MFR would become kink unstable when its twist exceeds 1.25 turns. However, both theories (Hood & Priest 1979, 1980Bennett et al 1999;Baty 2001;Török et al 2004;Török & Kliem 2005;Zaqarashvili et al 2010) and observations (Wang et al 2016;Liu et al 2019) and so on. Based on the previous works (Dungey & Loughhead 1954;Hood & Priest 1979;Bennett et al 1999;Baty 2001), the critical twist is proportional to the aspect ratio of an MFR, namely,…”

Observation and Modeling of Solar Jets

“…Specifically, the statistical studies made by Moore et al [64,186] found the existence of obvious axial rotation in both standard and blowout jets; their results showed that the number of turns of axial rotation ranges from 0.25 to 2.5. Other case studies showed that the number of turns of axial rotation ranges from about 0.34 to 4.7 [187][188][189][190], and the periods were measured to be 1-20 minutes [174,191,192]. The rotating motion of solar jets manifests as simultaneous blue-and redshift on the either side of the jet body in doppler velocity maps [88,108,[181][182][183]193].…”