A NEW METHOD FOR DIAGNOSTICS OF SOLAR MAGNETIC-FIELDS AND FLOWS FROM TIME-DISTANCE ANALYSIS

We propose a new method to obtain information on plasma flows and magn etic fields below the visible solar surface using time-distance measur ements. The method is based on sine and cosine transforms of propagati on times measured as a function of direction. The method allows one to sort out various characteristics of the subsurface medium, the flows, magnetic fields and their nonuniformities, and is less sensitive to t he measurement errors. We discuss the parity properties of various con tributions to the propagation times with respect to forward and backwa rd directions and show how these properties allow separation of the ef fects of magnetic held and flows, as well as separation of the horizon tal components from the vertical. It is shown that the first harmonics contain information on the direction and absolute value of the veloci ty, while the second harmonics are sensitive to the orientation and ab solute value of horizontal magnetic fields and spatial gradients of th e flow velocity. We discuss the effects of discrete mesh on the accura cy of measurements of the propagation time. An advantage of the method is in its intrinsic invariance with respect to the choice of the coor dinate frame. The method provides an automatic rule of assigning prope r weights to every observation points. We give estimates of the accura cy of the reconstruction of the flow held over distances comparable wi th the scale of the convection. We also present the ''magnetic'' corre ctions to the propagation time in a vertically stratified medium.