Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011spd....42.1707p&link_type=abstract
American Astronomical Society, SPD meeting #42, #17.07; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
We present results of resonant wave transformation in MHD models of sunspot. Numerical 3D MHD simulations of waves excited by subsurface point sources and traveling through the sunspot models reveal details of the MHD mode conversion, which happens in the regions where the wavefront crosses the level where the plasma parameter β is of the order of unity. In particular, the wave transformation produces slow MHD waves traveling predominantly along the magnetic lines in the central part of sunspot. This process is clearly seen when plotted as a projection of velocity (and magnetic field) variations along and perpendicular to the local direction of the magnetic field lines. Detailed simulations show that the transformed wave appears even in the case where the source is located completely outside the magnetic region, so that when the initial wave is pure acoustic. To investigate the wave amplitude and travel-time corrections due to the variations of thermodynamic properties and magnetic effects in sunspots we apply the 1D LTE radiation transfer code SPINOR/STOPRO to the wave simulation results. This permits us to simulate the profile of the HMI Fe6173A spectral line, and model the HMI observations of the line-of-sight velocity and magnetic field, and also the Stokes profiles. For calculation of the observables we use the same set of 6 narrow-band filters as used in the HMI instrument. Such simulations provide artificial HMI level-1 data for testing helioseismology measurements in sunspots and magnetic active regions.
Kosovichev Alexander
Parchevsky Konstantin
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