NUMERICAL-SIMULATION OF A RAIN SHOWER AFFECTED BY WASTE ENERGY RELEASED FROM A COOLING-TOWER COMPLEX IN A CALM ENVIRONMENT

An axisymmetric cloud model is used to investigate the evolution of co nvective cells and associated rain showers that develop due to the sen sible and latent heat released into a calm atmosphere from an industri al cooling complex. The simulated convection is in fair agreement with observations for a particular cloud developing over a large cooling s ystem. Sensitivity experiments were run for two different soundings to quantify how the convection and rainfall depend on the magnitude of t he waste energy loss, the area of the source region, and other paramet ers. The major findings were the following: 1) Without a sustained was te heat input the model convection ceased. The model convection became progressively more intense and developed more rain when the rate of t otal waste energy heat released from the power station was increased. Doubling the total waste energy amount from its control case value cau sed a 15-fold increase in 3-h rainfall values. However, reducing the c ontrol case value of total waste energy release by 20% led to much wea ker convection without rain. 2) The triggering of cumulus clouds was r educed when the waste energy was released in terms of latent heat rath er than sensible heat. As the relative contribution of sensible heat i ncreased, so did the intensity of the circulation and the rainfall. 3) The cloud formation depended on the area of the heat source: a wider source tended to delay and to weaken the convection. Specifically, whe n the area was doubled the simulated cloud appeared 2.5 min later and the total accumulated rain after 3 h was reduced by 88%. Moreover, the maximum total kinetic energy was reduced by 26%. 4) The model results were only slightly sensitive to the radial distribution of the sensib le and latent heat fluxes within the source region.