2014/11/21 by R. Soler, J. L. Ballester, T. V. Zaqarashvili · 1 citation
Physics and Astronomy · #Astronomy #Astrophysics #Atomic physics #Chromosphere #Collision frequency #Computational physics #Dissipation #Dissipative system #Ion #Ionosphere and magnetosphere dynamics #Millimeter #Optics #Physics #Plasma #Quantum mechanics #Solar and Space Plasma Dynamics #Spectral line #Stellar, planetary, and galactic studies #Wavelength #astro-ph.SR
paper · pdf · doi:10.1051/0004-6361/201423930
published as A&A 573, A79 (2015) · Accepted for publication in A&A
arxiv created 2014/11/21 · openalex publication_date 2014/11/24 · arxiv updated 2014/12/24 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Alfvénic waves are ubiquitous in the solar atmosphere and their dissipation may play an important role in atmospheric heating. In the partially ionized solar chromosphere, collisions between ions and neutrals are an efficient dissipative mechanism for Alfvén waves with frequencies near the ion-neutral collision frequency. The collision frequency is proportional to the ion-neutral collision cross section for momentum transfer. Here, we investigate Alfvén wave damping as a function of height in a simplified chromospheric model and compare the results for two sets of collision cross sections, namely those of the classic hard-sphere model and those based on recent quantum-mechanical computations. We find important differences between the results for the two sets of cross sections. There is a critical interval of wavelengths for which impulsively excited Alfvén waves are overdamped as a result of the strong ion-neutral dissipation. The critical wavelengths are in the range from 1 km to 50 km for the hard-sphere cross sections, and from 1 m to 1 km for the quantum-mechanical cross sections. Equivalently, for periodically driven Alfvén waves there is an optimal frequency for which the damping is most effective. The optimal frequency varies from 1 Hz to 102 Hz for the hard-sphere cross sections, and from 102 Hz to 104 Hz for the quantum-mechanical cross sections. Future observations at sufficiently high spatial or temporal resolution may show the importance of high-frequency Alfvén waves for chromospheric heating. For instance, the Atacama Large Millimeter/submillimeter Array (ALMA) may be able to detect the critical wavelengths and optimal frequencies and so to test the effective collision cross section in the chromospheric plasma.