THE DEPENDENCE OF THE DIFFUSION-COEFFICIENT ON THE MIXING LENGTH IN KATO OVERSTABLE ZONE

The treatment of the overstable zone by Langer, Sugimoto & Fricke is e xtended so that the effects of radiative heat loss from convective ele ments and of the mixing length are included. As the overstability inve stigated by Kato arises because of the radiative heat loss from the co nvective element, this loss may play a role in the heat flux. In the f ormulation presented in this work, the diffusion coefficient depends o n the mixing length when the mixing length is very small. In calculati ons with the method of Langer et al., the efficiency factor of the dif fusion coefficient of chemical species is sometimes much smaller than 1. This exceedingly small efficiency factor may be explained by the de pendence of the diffusion coefficient on the mixing length. We find th at the neutral condition of Kato's overstable zone is del(rad) = V-ad.