Overdense Threads in the Solar Corona Induced by Torsional Alfvén Waves

Abstract

High-resolution and high-cadence observations have shown that Alfvén waves are ubiquitous in the solar atmosphere. Theoretical works suggest their ability to transfer large energy fluxes from the photosphere to the corona and solar wind. In this proof-of-concept Letter we show that torsional Alfvén waves can induce the formation of filamentary plasma structures in the solar corona. We perform high-resolution 3D ideal MHD simulations in an initially uniform coronal plasma permeated by a line-tied twisted magnetic field. We find that torsional Alfvén waves develop Kelvin–Helmholtz instabilities as a result of the phase mixing process. The Kelvin–Helmholtz instability drives plasma compression that breaks the uniformity of density, creating elongated overdense threads aligned with the direction of the magnetic field. With synthetic modeling of SDO/AIA imaging we show that the overdense filaments could be seen in observations as fine strands that illuminate the underlying magnetic structure.

Numerical simulations of turbulence in prominence threads induced by torsional oscillations

“…Consequently, Alfvén modes at different radial positions in the flux tube become out of phase as time increases. This phenomenon is the well-known process of phasemixing (see, e.g., Heyvaerts & Priest 1983;Nocera et al 1984;De Moortel et al 2000;Smith et al 2007;Prokopyszyn et al 2019;Díaz-Suárez & Soler 2021a). Phase-mixing is a linear process that generates shear flows perpendicularly to the magnetic field lines and transports Alfvén wave energy from large to small perpendicular scales.…”