Computer Science – Sound
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006spd....37.0507z&link_type=abstract
American Astronomical Society, SPD meeting #37, #5.07; Bulletin of the American Astronomical Society, Vol. 38, p.224
Computer Science
Sound
Scientific paper
It was found recently by helioseismic holography analysis that magneticfields that are inclined relative to the line-of-sight direction couldcause systematic variations in measured acoustic phase shifts, andthe presence of surface magnetic field may shift the phases and impairthe coherence of acoustic waves, known as "showerglass effect". Weexamine how these two observational effects affect time-distancemeasurements in magnetic regions. It is confirmed that the inclinedmagnetic field could cause variations in measured travel times insidesunspot penumbra, however, inversions of the measured times showthat this effect only slightly shift the location of negativesound-speed variations near the solar surface, but basically does notchange the inverted deeper interior structures. Measurements by useof continuum intensitygrams and line-depth data illustrate that theinclined magnetic field does not cause any obvious systematic traveltime variations. For the showerglass effect, we find that the outgoingand ingoing travel time perturbations through sunspots from our typicaltime-distance measurements are significantly smaller than those reportedfrom holography, and also strongly depend on the propagation depths.Additionally, our second-skip travel time measurements demonstrate thatthe signals inside sunspots do not introduce detectable phase shiftsafter applying phase-speed filtering. We finally conclude that thesesurface magnetism effects do not cause considerable systematic errorsin time-distance helioseismology of active regions.
Kosovichev Aleksandr G.
Zhao Junwei
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