The interaction between acoustic waves and inclined magnetic fields near the β~1 layer

Details The interaction between acoustic waves and inclined magnetic fields near the β~1 layer The interaction between acoustic waves and inclined magnetic fields near the β~1 layer

Aug 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd..17e..16s&link_type=abstract

Highlights of Recent Progress in the Seismology of the Sun and Sun-Like Stars, 26th meeting of the IAU, Joint Discussion 17, 23

Computer Science

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Scientific paper

The acoustic showerglass effect may be hindering our helioseismic renditions of the solar subsurface. We present the results of near -surface wave conversion of acoustic waves in a model polytropic atmosphere by a uniform, inclined magnetic field. The upcoming fast, acoustic wave undergoes conversion to a slow, magnetic wave at the β ~ 1 layer where the sound speed and Alfven speed are comparable. The conversion is dependent upon the " attack angle" between the ray path and the magnetic field. The angle of the wave vectors at the polytropic " surface" is compared to observations of surface velocity vectors in sunspot penumbrae. AR9026 and AR9057 both have well- defined, static penumbrae and their Doppler velocities are viewed from different angles by SOHO-MDI as they cross the solar disk. The phase of the correlation between the ingression and surface velocity, determined by helioseismic holography, is used to assess the effect the penumbral magnetic field has on incoming acoustic waves. The phase is found to be dependent upon the line-of-sight of observation indicating that this is a surface phenomenon, which could otherwise be interpreted as subsurface travel-time perturbations of up to one minute. Furthermore, using vector magnetograms from the IVM at the Mees Observatory, the phase of the correlation is found to be dependent on the magnetic field tilt from vertical, and the dependence is consistent across the two sunspots. Comparing the results from the polytropic model with the observations show strong support for the near-surface wave conversion theory, although many questions still remain.

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