条件付不安定成層中の微小振幅対流

Abstract

The properties of small-amplitude convection in the conditionally unstable stratification of the atmosphere which have been studied by Kuo (1961, 1965) are re-examined by the use of the finite difference method which implicitly introduces the condition for the continuity of the horizontal gradient of temperature at the internal boundary between an ascending region and adescending region. This condition, which was not used by Kuo, is required for the finiteness of the horizontal eddy thermal diffusivity term which is assumed to be of the Fickian type. It is shown that when the horizontal size of a convective cell as well as some physical parameters are specified, the horizontal size of an ascending area is uniquely determined. This property is markedly contrasted with the property of convection for the non-viscous case (Haque, 1952; Lilly, 1960) where the size of an ascending area is not uniquely determined.The use of the finite difference method enables us to discuss the properties of unstable convection. The dependencies of the growth rate and other properties of convection on physical parameters are studied.The properties of convection is also studied as an initial value problem. Furthermore, it is shown that this approach is very useful to obtain an eigensolution, particularly when the separation of variables with respect to the horizontal and vertical coordinates is impossible.