Numerical Experiment of the Development of a Cumulus Convection
Journal of the Meteorological Society of Japan
As a step to study the ensemble effect of cumuli on larger scale disturbances, the development of an averaged cumulus convection is numerically simulated by using the model based on the 2-column model devised by Asai and Kasahara (1967). Two cases are taken up. In the first case, the radius of the inner cloud column is fixed during the calculation regardless to the development of the cloud. The effect of the drag force of the condensed water droplets on the motion is specifically estimated. It
... ally estimated. It is shown that the effect of the drag force suppresses considerably the maximum height of cloud top, the maximum value of vertical velocity and the maximum anormalies of other meteorological field variables such as potential temperature, water vapor and liquid water. However, the life time of the convection remains unaltered. If we assume that all the condensed liquid water is instantaneously taken out of the atmosphere by precipitation, the life time is a little shortened and the vertical heat transport is more or less decreased. In the second case, the inner cloud column is allowed to change its radius according to development of the cloud. Although the same effect of the drag force as in the first case is also incorporated in this case, the changeability of radius of inner cloud column results in the increase of thermal activity of the convection, even overcoming the suppressing effect due to the drag force. The life time in this case is a little larger than in the first case. In each case, the total heat transport per unit area during forty minutes is calculated as a measure of the thermal activity of convection. For several horizontal scales calculated, the maximum values of the heat transport are attained at almost similar values of the ratio of the radius of inner cloud column to that of the whole column in both cases.