Waves in magnetic flux concentrations: The critical role of mode mixing and interference

Details Waves in magnetic flux concentrations: The critical role of mode mixing and interference Waves in magnetic flux concentrations: The critical role of mode mixing and interference

Jul 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002an....323..196b&link_type=abstract

Astronomische Nachrichten, vol. 323, no. 3/4, p. 196-202

Astronomy and Astrophysics

Astronomy

22

Stars: Oscillations, Stars: Spots, Sun

Scientific paper

Time-dependent numerical simulations of nonlinear wave propagation in a two-dimensional (slab) magnetic field geometry show wave mixing and interference to be important aspects of oscillatory phenomena in starspots and sunspots. Discrete sources located within the umbra generate both fast and slow MHD waves. The latter are compressive acoustic waves which are guided along the magnetic field lines and steepen into N-waves with increasing height in the spot atmosphere. The former are less compressive, and accelerate rapidly upward through the overlying low-beta portion of the umbral photosphere and chromosphere (beta equiv 8pi p/ B2). As the fast wave fronts impinge upon the beta ~ 1 penumbral ``magnetic canopy" from above, they interfere with the outward-propagating field-guided slow waves, and they also mode convert to (non-magnetic) acoustic-gravity waves as they penetrate into the weak magnetic field region which lies between the penumbral canopy and the base of the surrounding photosphere. In a three-dimensional situation, one expects additional generation, mixing and interference with the remaining torsional Alfvén waves.

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