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
