A large eddy simulation (LES) model has been used to simulate a convective boundary layer over a uniform plain. The aim of this study is to investigate the large eddy structure, their temporal development and the momentum transfer between the upper and lower layers. The inital condition of the potential temperature within the mixing layer is constant and the potential temperature gradient of the upper stable layer is assumed constant (= 3.5 K km-1). The profile of basic flow is horizontally homogeneous or zero, and the boundary condition on the bottom is given by a uniformaly latent heat flux on the flat surface.
When the basic flow is zero, initial disturbances gradually grows up, and the organized structure of turbulent flow is found in the early development stages that is a single eddy of regional size. It is shown that the vertical convection and the entrainment are effective when the basic flow is weak or zero. When the basic flow is horizontally averaged, the turbulence is confined to the lower convective boundary layer. It is also shown that the basic flow suppresses the vertical convection and the entrainment in the upper layer.