**Previous
abstract** **Next
abstract**

**Session 79 - Quiet Solar Photosphere and Chromosphere.**

*Oral session, Thursday, June 13*

*Playcircle, *

## [79.02] A New Method for Diagnostics of Subsurface Magnetic Fields and Flows from Time-Distance Analysis

*M. Ryutova (Stanford Univ.)*
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.

References

Duvall, T..L.Jr., S.M.Jefferies, J.W. Harvey and M.A.Pomerantz, 1993,
Nature, 362, 430.

**Program
listing for Thursday**