On the Origins of Coronal Alfvénic Waves

Abstract

[eng] Alfvénic waves are considered a key contributor to the energy flux that powers the Sun’s corona, with theoretical models demonstrating their potential to explain coronal EUV and X-ray emission and the acceleration of the solar wind. However, confirming underlying assumptions of the models has proved challenging, especially obtaining evidence for the excitation and dissipation of Alfvénic waves in the lower solar atmosphere and tracing their propagation into the corona. We present an investigation of the Alfvénic wave power spectrum in the Sun’s corona, obtained from observations with DKIST Cryo-NIRSP. The data provide unprecedented temporal resolution and signal-to-noise ratio, revealing a detailed power spectrum out to frequencies exceeding 10 mHz. A broad enhancement in power dominates the spectrum, and we demonstrate that it is accurately reproduced using a physics-based model. The results corroborate the scenario where the corona is dominated by Alfvénic waves excited in the photosphere by horizontal convective motions, with low-frequency waves subject to reflection at the transition region and higher-frequency waves significantly dissipated by the partially ionized chromosphere. The coronal Alfvénic power spectrum also indicates that there are contributions from p-modes (via mode conversion) and a yet-unknown higher-frequency source. These results provide key insight into how the Sun’s convective motions imprint themselves on the corona and highlight the critical role of partial ionization, reflection, and damping in regulating upward-propagating Alfvénic waves. A further implication of this is that reconnection-driven Alfvénic waves likely play a smaller role in powering the corona and solar wind than has been suggested by recent studies.