Three-Dimensional Simulations of Tearing and Intermittency in Coronal Jets

Abstract

Observations of coronal jets increasingly suggest that local fragmentation and intermittency play an important role in the dynamics of these events. In this work, we investigate this fragmentation in high-resolution simulations of jets in the closed-field corona. We study two realizations of the embedded-bipole model, whereby impulsive helical outflows are driven by reconnection between twisted and untwisted field across the domed fan plane of a magnetic null. We find that the reconnection region fragments following the onset of a tearing-like instability, producing multiple magnetic null points and flux-rope structures within the current layer. The flux ropes formed within the weak-field region in the center of the current layer are associated with "blobs" of density enhancement that become filamentary threads as the flux ropes are ejected from the layer, whereupon new flux ropes form behind them. This repeated formation and ejection of flux ropes provides a natural explanation for the intermittent outflows, bright blobs of emission, and filamentary structure observed in some jets. Additional observational signatures of this process are discussed. Essentially all jet models invoke reconnection between regions of locally closed and locally open field as the jet-generation mechanism. Therefore, we suggest that this repeated tearing process should occur at the separatrix surface between the two flux systems in all jets. A schematic picture of tearing-mediated jet reconnection in three dimensions is outlined.

Formation and Reconnection of Three-dimensional Current Sheets with a Guide Field in the Solar Corona

“…The representative magnetic field lines in the Figure 9 visualizations show the increasing flux rope sizes in the plane of the current sheet. Wyper et al (2016) described the formation and evolution of 3D magnetic island flux ropes during the reconnection associated with coronal jets and essentially the same picture holds for our extended pseudostreamer arcade as well. Reconnection forms a localized region of highly twisted field in the 3D magnetic island but the field lines that make up this newly-reconnected open flux tube are relatively untwisted far from the current sheet.…”

“…Reconnection forms a localized region of highly twisted field in the 3D magnetic island but the field lines that make up this newly-reconnected open flux tube are relatively untwisted far from the current sheet. Therefore, the twist itself will propagate away as torsional Alfvénic waves from the reconnection site in both directions in an attempt to spread out along the field lines as much as possible (see §5.2 and Figure 9 of Wyper et al 2016). These Alfvénic fluctuations propagate both down the flux tube toward the lower boundary and along the direction of the flux tube that opens up into the solar wind.…”

“…ARMS has been used to study numerous dynamic phenomena in the solar atmosphere, including coronal jets (Pariat et al 2015;Wyper et al 2016;Karpen et al 2017), theinteraction between closed and open fields at streamer boundaries (Edmondson et al 2009(Edmondson et al , 2010aMasson et al 2013;Higginson et al 2017a,b), and the examination of plasmoid-unstable reconnection and magnetic island evolution (Paper I; Guidoni et al 2016;Lynch et al 2016). …”

A universal model for solar eruptions

“…This is the highest-resolution adaptive-mesh calculation of its type to date, and it clearly resolves for the first time different stages of the mini-CME jet. The setup is similar to our previous calculations 15,16 (see methods section for details). To represent an emerged bipolar region in a solar coronal hole, we start with a strong bipole embedded in an inclined, uniform, ambient field ( Figure 1a).…”

Three-dimensional magnetic reconnection and its application to solar flares

“…Therefore, it remains difficult to properly address the physics of the current layer evolution, with respect to the development of instabilities such as the tearing mode. Recent investigations by Nishida, Nishizuka & Shibata (2013) and Wyper et al (2016) show studies of the behaviour of the 3-D current layer, with multiple shredding and plasmoid formation as would be expected from the 2-D well-studied evolution. However, the complexity of the configuration in three dimensions (see figure 4 in Nishida et al (2013)) shows that it is difficult to properly define the equivalent of magnetic islands seen in two dimensions.…”