Evolution of Kelvin–Helmholtz Instability in the Fan-spine Topology

Abstract

We use multiwavelength imaging observations from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory to study the evolution of the Kelvin–Helmholtz (K–H) instability in a fan-spine magnetic field configuration. This magnetic topology exists near an active region AR12297 and is rooted in a nearby sunspot. In this magnetic configuration, two layers of cool plasma flow in parallel and interact with each other inside an elongated spine. The slower plasma flow (5 km s−1) is the reflected stream along the spine’s field lines from the top, which interacts with the impulsive plasma upflows (114–144 km s−1) from below. This process generates a shear motion and subsequent evolution of the K–H instability. The amplitude and characteristic wavelength of the K–H unstable vortices increase, satisfying the criterion of the fastest-growing mode of this instability. We also describe how the velocity difference between two layers and the velocity of K–H unstable vortices are greater than the Alfvén speed in the second denser layer, which also satisfies the criterion of the growth of the K–H instability. In the presence of the magnetic field and sheared counterstreaming plasma as observed in the fan-spine topology, we estimate the parametric constant Λ ≥ 1, which confirms the dominance of velocity shear and the evolution of the linear phase of the K–H instability. This observation indicates that in the presence of complex magnetic field structuring and flows, the fan-spine configuration may evolve into rapid heating, while the connectivity changes due to the fragmentation via the K–H instability.

Dimensionality of solar magnetic reconnection

“…Such filament eruption within the closed fan may occur under ideal MHD instabilities, e.g. kink and torus instabilities (Lee et al 2016a;Li et al 2018b;Mishra et al 2021;Howson et al 2021). Not only the resistive reconnection but the ideal MHD instabilities should therefore be integrated into the 3D null reconnection in a fan-spine structure.…”

Alfvén pulse driven spicule-like jets in the presence of thermal conduction and ion-neutral collision in two-fluid regime

“…These cool spicule-like jets are significant dynamical plasma processes that may be accompanied by various types of waves, oscillations, instabilities etc. in the Sun's atmosphere [5,6,[9][10][11][12][13]. Such confined and cool jet like features may be one of the possible sources to carry energy and mass from the inner layers (i.e.…”

Origin of Quasi-periodic Pulsation at the Base of a Kink-unstable Jet

“…The physical process used in the untwisting models (i.e., reconnection between the twisted magnetic field and open magnetic field lines) is not the only way to trigger the solar jets and their helical or rotating motions. Various types of magnetohydrodynamic (MHD) instabilities (e.g., Rayleigh-Taylor (RT), Kelvin-Helmholtz (KH), Ballooning mode, convective-driven instability, radiatively driven instability, heat-driven thermal instabilities, tearing mode, kink mode, sausage mode, helical/torsional mode, and current-sheet mode) are important physical processes that trigger the wide varieties of the solar phenomena, i.e., from small-scale events (e.g., solar jets) to large-scale eruptions (Mishra et al 2018;Mishra & Srivastava 2019;Mishra et al 2021). Kink instability is one of the prominent mechanisms to trigger the solar jets (see the review within Raouafi et al 2016).…”