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Paper: The Role of MHD Mode Conversion in Sunspot Seismology
Volume: 354, Solar MHD Theory and Observations: A High Spatial Resolution Perspective
Page: 161
Authors: Crouch, A.D.; Cally, P.S.; Charbonneau, P.; Braun, D.C.; Desjardins, M.
Abstract: Sunspots absorb energy from and shift the phase of f and p modes incident upon them. Understanding the mechanism causing each of these effects is vital to the local helioseismology of sunspots (and magnetic flux concentrations in general). Because the beta-equals-unity layer typically lies in the near surface layers below the photospheres of sunspot umbrae, MHD mode conversion can occur. Mode conversion provides a promising absorption mechanism because the slow magnetoacoustic-gravity waves and Alfven waves guide energy along the magnetic field away from the acoustic cavity. Our previous mode conversion calculations have shown that simple sunspot models with non-vertical magnetic fields can produce ample absorption to explain the Hankel analysis measurements, along with phase shift predictions that agree well with the observations. Those calculations only considered the possibility of MHD waves propagating down the magnetic field into the interior. In this contribution, we consider a second additional possibility – waves propagating up into the atmosphere overlying sunspots.
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