Understanding Dynamical Properties of Cumulus Clouds over the Bay of Bengal

An idealized large eddy simulation (LES) has been performed to understand the dynamics of cumulus clouds over the Bay of Bengal using the Weather Research and Forecasting (WRF) model. Cumulus clouds play a key role in the atmospheric convection process. However, despite their importance, they are not well represented in global climate models (GCMs). Moreover, cumulus clouds involve a transition from shallow to deep clouds (or congestus clouds), and GCMs are unable to capture this phenomenon. The development of cumulus clouds is very pronounced over the Bay of Bengal region, and its dynamics has not yet been fully explored. In the present study, a gradual transition phenomenon of shallow cumulus to deep cumulus (congestus) at the development stage and understanding the evolution of clouds and flux transport is investigated. Different cloud parameters at shallow and deep cumulus congestus stages are examined. It is observed that the shallow clouds have a higher magnitude of entrainment than that of deep clouds, and the rate of decrease in entrainment with height is also higher for the shallow clouds. Moreover, the detrainment rate is higher in the case of shallow cumulus clouds as well. This means that as the clouds have transitioned from shallow cumulus to deep congestus clouds, both entrainment and detrainment rates decrease. This important finding will be quite useful in developing future parameterizations for cumulus clouds. A negative correlation between the entrainment rate and cloud core vertical velocity is observed which is supported by previous studies.