Acoustic response to transverse oscillations in a solar coronal loop

Abstract

Context. Magnetohydrodynamic (MHD) waves play an important role in the dynamics and heating of the solar corona. Their investigation also reveals information about the local conditions. Transverse (Alfvénic) oscillations of loops commonly occur in response to solar eruptions. It has been shown that these oscillations elicit an acoustic response through wave coupling at the footpoint and the pondermotive force. Aims. We extend the modelling of wave coupling between a transverse loop oscillation and slow magnetoacoustic waves through line-tied footpoint boundary conditions by considering the effect of transverse loop structuring and nonlinearity. Methods. We combine analytical wave modelling with fully nonlinear MHD simulations to study the wave field of propagating slow waves in a two-dimensional slab loop (arcade) model. Results. We demonstrate that transverse loop oscillations generate propagating slow waves from both footpoint with the same periodicity but shorter wavelength determined by the local sound speed. The degree of wave coupling is proportional to the square root of the plasma-β. The slow wave field is anti-symmetric in the direction of transverse wave polarisation. We show through synthetic diagnostics that this has important consequences for their observability in terms of the orientation of the loop with respect to the observer. We also show that for the interpretation of intensity oscillations associated with typical loop oscillations the ponderomotive response also needs to be taken into account. The modelling presented here allows for the successful identification of the slow waves and pondermotive response in a previous observational study.

Flare quasi-periodic pulsation associated with recurrent jets

“…The observed QPPs could provide the time feature and plasma characteristic of flare emissions, which are helpful for diagnosing plasma properties on the Sun or Sun-like stars, especially at the flare location (Pugh et al, 2019;Zimovets et al, 2021b). When considering that flare QPPs are modulated by MHD waves, they might potentially lead to coronal heating through dissipating of those waves (Reale et al, 2019;Van Doorsselaere et al, 2020;White and Verwichte, 2021;. Moreover, they can allow us to map coronal magnetic fields and estimate plasma parameters in the corona, named as 'coronal seismology' (e.g., Yang et al, 2020;Anfinogentov et al, 2022).…”