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Session 79 - Quiet Solar Photosphere and Chromosphere.
Oral session, Thursday, June 13
We propose a new method of obtaining the information on plasma flows and magnetic fileds below the visible surface using the time-distance measurements. The recent advent of time-distance tomography (Duvall et al. 1993) consisting in the discovery that allows to measure directly the travel time between any point on the solar surface and a surrounding annulus, opens the efficient ways to study the structure and dynamics of the solar interior. We suggest to use sin n\theta and cos n\theta convolutions of the propagation time \tau_\theta measured between any point inside the annulus with the prescribed azimuthal angle \theta: \beginequation \bar \tau_c^(n)\;=\;\frac12\pi\int\limits_0^2\pi \tau(\theta)\cos n\theta d\theta \qquad \bar \tau_s^(n)\;=\;\frac12\pi\int\limits_0^2\pi \tau(\theta)\sin n\theta d\theta \endequation Using the approximation of geometrical acoustics and assuming that the magnetic effects are small, we find that the first harmonics (n=1) contain an information predominantly on the direction and absolute value of the horizontal flow velocity, while the second harmonics (n=2) predominantly describes orientation and absolute value of the horizontal magnetic field. The data obtained for the different annuli give a topology and absolute values of the mass flows and magnetic fields at the different depths. We discuss the effects of discrete mesh on the accuracy in measurements of propagation time. The advantage of the method consists in the fact that we do not need any specific choice of the measurement mesh; the method itself establishes a rule by which one can use any a priori chosen mesh to find the distribution of horizontal magnetic fields and flows.
This research is supported by NASA contract NAG5-3077 at Stanford University.
Duvall, T..L.Jr., S.M.Jefferies, J.W. Harvey and M.A.Pomerantz, 1993, Nature, 362, 430.
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