In-situ generation of transverse MHD waves from colliding flows in the solar corona

Abstract

Transverse MHD waves permeate the solar atmosphere and are a candidate for coronal heating. However, the origin of these waves is still unclear. In this work, we analyse coordinated observations from \textit{Hinode}/SOT and \textit{IRIS} of a prominence/coronal rain loop-like structure at the limb of the Sun. Cool and dense downflows and upflows are observed along the structure. A collision between a downward and an upward flow with an estimated energy flux of $10^7-10^8$~erg~cm${}^{-2}$~s${}^{-1}$ is observed to generate oscillatory transverse perturbations of the strands with an estimated $\approx 40$km~s${}^{-1}$ total amplitude, and a short-lived brightening event with the plasma temperature increasing to at least $10^5$K. We interpret this response as sausage and kink transverse MHD waves based on 2D MHD simulations of plasma flow collision. The lengths, density and velocity differences between the colliding clumps and the strength of the magnetic field are major parameters defining the response to the collision. The presence of asymmetry between the clumps (angle of impact surface and/or offset of flowing axis) is crucial to generate a kink mode. Using the observed values we successfully reproduce the observed transverse perturbations and brightening, and show adiabatic heating to coronal temperatures. The numerical modelling indicates that the plasma $\beta$ in this loop-like structure is confined between $0.09$ and $0.36$. These results suggest that such collisions from counter-streaming flows can be a source of in-situ transverse MHD waves, and that for cool and dense prominence conditions such waves could have significant amplitudes.

arXiv commentAccepted for publication in The Astrophysical Journal Letters

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Cited by in corpus (8)

• Coronal heating by MHD waves
• Kink oscillations of coronal loops
• Probing the physics of the solar atmosphere with the Multi-slit Solar Explorer (MUSE): I. Coronal Heating
• Magnetohydrodynamic Fast Sausage Waves in the Solar Corona
• Contribution of observed multi frequency spectrum of Alfvén waves to coronal heating
• Fast Magnetosonic Waves and Flows in a Solar Prominence Foot: Observations and Modeling
• MHD simulations of the in-situ generation of kink and sausage waves in the solar corona by collision of dense plasma clumps
• Effects of external flow on resonant absorption of coronal loop kink oscillations driven by an external fast wave: Selective excitation problem