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Detection of Phase Travel Time Anisotropy from Subsurface Horizontal Magnetic Fields in the Sun

Presentation #350.14 in the session The Sun and the Solar System — iPoster Session.

Published onJun 29, 2022
Detection of Phase Travel Time Anisotropy from Subsurface Horizontal Magnetic Fields in the Sun

We derive a helioseismic measurement technique which isolates phase travel time deviations caused by horizontal magnetic fields from other contributions such as sound speed perturbations and flows. The technique also allows for the azimuth of the subsurface magnetic field to be determined in addition to a direct proxy for the horizontal field’s magnitude. We validate this technique using two independent MHD simulations. The first model simulates propagation of acoustic waves from a point source in a uniform, inclined magnetic field, and we recover the correct azimuth and the expected travel time anisotropy from ray theory. The second model simulates a realistic sunspot with non-uniform magnetic field, where we find the anisotropy and azimuth of the subsurface magnetic field. Finally, we apply the technique to several active regions observed by HMI (Helioseismic and Magnetic Imager) and examine characteristics of the subsurface horizontal magnetic field at depths z=-5 to -7 Mm, -7 to -10 Mm, and -10 to -13 Mm.

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