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Properties of p and f modes in hydromagnetic turbulence
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.ORCID iD: 0000-0002-7304-021X
2015 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 447, no 4, 3708-3722 p.Article in journal (Refereed) Published
Abstract [en]

With the ultimate aim of using the fundamental or f mode to study helioseismic aspects of turbulence-generated magnetic flux concentrations, we use randomly forced hydromagnetic simulations of a piecewise isothermal layer in two dimensions with reflecting boundaries at top and bottom. We compute numerically diagnostic wavenumber-frequency diagrams of the vertical velocity at the interface between the denser gas below and the less dense gas above. For an Alfven-to-sound speed ratio of about 0.1, a 5 per cent frequency increase of the f mode can be measured when k(x)H(p) = 3-4, where k(x) is the horizontal wavenumber and H-p is the pressure scaleheight at the surface. Since the solar radius is about 2000 times larger than H-p, the corresponding spherical harmonic degree would be 6000-8000. For weaker fields, a k(x)-dependent frequency decrease by the turbulent motions becomes dominant. For vertical magnetic fields, the frequency is enhanced for k(x)H(p) approximate to 4, but decreased relative to its nonmagnetic value for k(x)H(p) approximate to 9.

Place, publisher, year, edition, pages
2015. Vol. 447, no 4, 3708-3722 p.
Keyword [en]
MHD-turbulence, waves, Sun: helioseismology, Sun: magnetic fields
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-163443DOI: 10.1093/mnras/stu2540ISI: 000350273400058OAI: oai:DiVA.org:kth-163443DiVA: diva2:801082
Funder
Swedish Research Council, 621-2011-5076 2012-5797EU, European Research Council, 227952
Note

QC 20150408

Available from: 2015-04-08 Created: 2015-04-07 Last updated: 2017-12-04Bibliographically approved

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Brandenburg, Axel

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Singh, Nishant K.Brandenburg, Axel
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