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Paper: Signatures of Seismic Absorption in Magnetic Regions
Volume: 383, Subsurface and Atmospheric Influences on Solar Activity
Page: 141
Authors: Lindsey, C.; Cally, P.S.
Abstract: One of the major developments in local helioseismology of the late 1980s was the discovery by Braun, Duvall, & LaBonte that magnetic regions strongly absorb p modes that the quiet Sun itself efficiently reflects. A second major development, in the mid 1990s with the advent of the Solar and Heliospheric Observatory, was the discovery by Duvall et al. that phase travel times for waves propagating into sunspot photospheres are significantly longer than for waves propagating away from them along identical paths, a phenomenon to which we refer in this review as “the phase asymmetry.” Theoretical work by Cally et al. proposes to explain absorption of p modes by coupling of p modes to Alfvén modes. Recent work by Schunker et al. shows compelling evidence that this coupling contributes strongly to the phase asymmetry. More recent work by Rajaguru et al. suggests that radiative transfer effects in magnetic photospheres with upward-propagating waves contribute significantly to the phase asymmetry. Both of these contributions depend on strong absorption of p modes in magnetic photospheres. We will comment on the physics that relates phase shifts that underlie phenomena such as the phase asymmetry to irreversible processes such as p-mode absorption in magnetic regions. Magnetic contributions to the phase asymmetry have significant implications respecting seismic diagnostics of flows in active region subphotospheres.
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