Spectral signatures of torsional Alfvén waves in synthetic Hα
Year: 2026
Type: article
Abstract: Torsional Alfvén waves are of particular interest because they can transport substantial energy from the lower solar atmosphere into the corona and therefore may contribute to coronal heating. However, their observational identification is challenging because the perturbations are predominantly rotational, which makes the development of reliable diagnostics essential. We investigated whether the Hα spectral line can serve as a diagnostic for detecting signatures of torsional Alfvén waves in the solar chromosphere. We performed a case study using synthetic Hα spectra generated from a 3D radiative magnetohydrodynamic (MHD) simulation of a solar plage region. We analyzed the temporal evolution of the line profiles together with the underlying MHD variables and examined the magnetic topology of the structure through field-line tracing. Tracing individual magnetic field lines in the region of interest shows that the wave excitation is triggered by the merging of two magnetic features of the same polarity, while persistent small-scale photospheric motions generate the twist. The subsequent rapid unwinding of magnetic field lines is accompanied by strands of enhanced heating at higher altitudes along the structure. Analysis of the Hα formation indicates that the blue wing reliably traces the primary upflow and samples approximately the same plasma over a limited interval during the event. In contrast, the red wing receives contributions from more spatially variable layers, typically located below the blue-wing formation height. Torsional motions can imprint signatures in Hα spectra, but these diagnostics probe only a limited part of the underlying dynamics. Robust identification of torsional Alfvén waves therefore requires systematic comparisons between spectral observations and realistic MHD simulations.
Source: Astronomy and Astrophysics
Authors: M. Skan, S. Danilovic
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W7220419918