Volume 649, May 2021
|Number of page(s)||7|
|Section||The Sun and the Heliosphere|
|Published online||02 June 2021|
A novel approach to identify resonant MHD wave modes in solar pores and sunspot umbrae: B − ω analysis
ASI, Italian Space Agency, Via del Politecnico snc, 00133 Rome, Italy
2 Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
3 Department of Physics and Astronomy, California State University Northridge, Northridge, CA 91330, USA
4 Plasma Dynamics Group, School of Mathematics and Statistics, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK
5 Plasma Dynamics Group, Department of Automatic Control and Systems Engineering, The University of Sheffield, Sheffield S1 3JD, UK
6 ESA Science and Operations Department, NASA/GSFC Code 671, Greenbelt, MD 20771, USA
7 Rosseland Centre for Solar Physics, University of Oslo, PO Box 1029, Blindern 0315, Oslo, Norway
8 Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, Blindern 0315, Oslo, Norway
9 INAF-OAR National Institute for Astrophysics, Monte Porzio Catone, RM 00041, Italy
10 Department of Physics, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
11 Mathematics and Statistic Department, Faculty of Science, King Faisal University, Al-Hassa, PO Box 400, Hofuf 31982, Saudi Arabia
12 Department of Physics and Astronomy, Georgia State University, Georgia, GA 30303, USA
13 Institute for Astronomy, University of Hawaii, Hawaii, HI 96768-8288, USA
14 Departament de Física, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain
15 Institut d’Aplicacions Computacionals de Codi Comunitari (IAC 3), Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain
Accepted: 9 March 2021
The umbral regions of sunspots and pores in the solar photosphere are generally dominated by 3 mHz oscillations, which are due to p-modes penetrating the magnetic region. In these locations, wave power is also significantly reduced with respect to the quiet Sun. However, here we study a pore where not only is the power of the oscillations in the umbra comparable to, or even larger than, that of the quiet Sun, but the main dominant frequency is not 3 mHz as expected, but instead 5 mHz. By combining Doppler velocities and spectropolarimetry and analysing the relationship between magnetic field strength and frequency, the resultant B − ω diagram reveals distinct ridges that are remarkably clear signatures of resonant magneto-hydrodynamic (MHD) oscillations confined within the pore umbra. We demonstrate that these modes, in addition to velocity oscillations, are also accompanied by magnetic oscillations, as predicted from MHD theory. The novel technique of B − ω analysis proposed in this article opens up an exciting new avenue for identifying MHD wave modes in the umbral regions of both pores and sunspots.
Key words: Sun: atmosphere / Sun: magnetic fields / Sun: photosphere / Sun: oscillations
© ESO 2021
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