Abstract
The interaction between small-scale convections and large-scale flow in the airmass transformation processes is investigated by making use of a numerical model. In the model a uni-directional large-scale wind is assumed. Fine resolution is used in the cross-stream and vertical directions in order to treat explicitly the convections transporting heat, mois-ture and momentum in the transformed layer, while coarse resolution is used in the down-stream direction to represent the slow evolution of the large-scale flow. The average profiles of potential temperature, specific humidity and velocity indicate that the transformed layer forms a moist convectively mixed layer characterized by a multiple-layer structure. When the sea surface temperature rises in the downstream direction, a pressure drop in that direction is produced by the convective heating, and the acceleration due to the pressure gradient force is balanced mainly with the deceleration due to the frictional force induced by the convective momentum flux. Because the excess of the pressure gradient force over the frictional force produces a mean downward motion, the development of the mixed layer is suppressed. Because the suppression is brought about by the convective heating which develops the mixed layer, the process can be called a negative feedback process.
