A new model for the lower overshoot layer in the Sun

Abstract

We present a model for the lower overshoot layer of the Sun, based on the realistic solar stratification, without the use of a "mixing-length" parameter, by solving the system of Reynolds momentum equations using the closure formalism of Canuto & Dubovikov (1997, 1998). A fixed value of velocity anisotropy is assumed, and the local convection model is assumed to be valid for the convectively unstable layer. In accordance with seismic constraints, overshoot (defined as the amount by which the convectively mixed zone extends beyond its boundary in local theory) is found to be as low as about 6 percent of the pressure scale height, and it is not bounded by a discontinuity from below.