Properties of p- and f-modes in hydromagnetic turbulence
Nordita Astrophysics seminars
Wednesday 09 April 2014
to 14:15 at
Nishant Singh (Nordita)
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 piecewiese isothermal layer in two dimensions with reflecting boundaries on 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% frequency increase of the f-mode can be measured when kx Hp = 3-4, where kx is the horizontal wavenumber and Hp the pressure scale height at the surface. The solar radius is 2000 times larger than Hp, so the corresponding spherical harmonic degree would be 6000-8000. For weaker fields, a frequency decrease by the turbulent motions becomes dominant. For vertical magnetic fields, the frequency is enhanced for kx Hp ~ 4, but decreased relative to its nonmagnetic value for kx Hp ~ 9.