Evolution of Kelvin-Helmholtz Instability in the Fan-Spine Topology

TL;DR

This study observes the development of Kelvin-Helmholtz instability in a fan-spine magnetic topology near an active solar region, revealing how plasma flows and magnetic fields interact to produce vortex structures and potential heating effects.

Contribution

It provides the first detailed observational analysis of Kelvin-Helmholtz instability evolution within a fan-spine magnetic configuration using multiwavelength imaging data.

Findings

Kelvin-Helmholtz vortices grow in amplitude and wavelength, satisfying instability criteria.

Velocity differences and vortex speeds exceed the Alfvén speed, confirming instability growth.

The magnetic and flow conditions favor the linear phase of Kelvin-Helmholtz instability.

Abstract

We use multiwavelength imaging observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) to study the evolution of 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 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 that the velocity difference between two layers and velocity of K-H unstable vortices are greater than the Alfven speed in the second denser layer, which also satisfies the criterion of the growth of K-H instability. In the presence of the magnetic field and sheared counter streaming plasma as observed in the fan-spine topology, we estimate the parametric constant, $\Lambda\ge$1, that 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.