Properties of $p$- and $f$-modes in hydromagnetic turbulence

Abstract

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 Alfvén-to-sound speed ratio of about 0.1, a 5% frequency increase of the $f$-mode can be measured when $k_x{H}_{\mathrm{p}}=3$-$4$, where $k_x$ is the horizontal wavenumber and $H_{\mathrm{p}}$ is the pressure scale height at the surface. Since the solar radius is about 2000 times larger than $H_{\mathrm{p}}$, 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 $k_x{H}_{\mathrm{p}}\approx 4$, but decreased relative to its nonmagnetic value for $k_x{H}_{\mathrm{p}}\approx 9$.

arXiv comment17 pages, 22 figures, Version accepted in MNRAS

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Cited by in corpus (5)

• High-wavenumber solar $f$-mode strengthening prior to active region formation
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• Absorption of high frequency oscillations and its relation to emissivity reduction
• Effects of Dynamo-Generated Large-Scale Magnetic Fields on the Surface Gravity ($f$) Mode
• Solar-Cycle Variation of quiet-Sun Magnetism and Surface Gravity Oscillation Mode