Mode Mixing by a Shallow Sunspot |
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Authors: | Barnes G. Cally P.S. |
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Affiliation: | (1) Department of Mathematics and Statistics, Monash University, P.O. Box 28M, Victoria , 3800, Australia;(2) Department of Mathematics and Statistics, Monash University, P.O. Box 28M, Victoria , 3800, Australia |
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Abstract: | Sunspots are strong absorbers of f and p modes. A possible absorption mechanism is direct conversion to slow magnetoacoustic waves. Calculations based on vertical magnetic field models show that this works well for f modes, but is inadequate for p modes. Using a very simple shallow spot model, in which the effects of the magnetic field are accounted for solely by a surface condition, we investigate the possibility that p modes first scatter into f modes inside the spot, which are then more susceptible to conversion to slow modes. We find that the coupling between an incident p mode and the internal f mode is unlikely to be strong enough to account for the observed absorption, but that the incident modes do couple strongly to the acoustic jacket in some cases, leading to a region immediately around the sunspot where a significant fraction of the surface velocity is due to the jacket modes. |
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