A diagnostic study of subgrid‐scale activation

Using large‐eddy simulations (LESs) of six observed boundary layer cases as benchmark data sets, we diagnosed vertical velocity as the sum of the grid‐mean () and the subgrid‐scale w using an empirical method we have developed. We have found that the subgrid‐scale w is best characterized by the root‐mean square of w ′ 2 . The vertical velocity is expressed in the form of w = + c , where c is diagnosed from LES data to be 0.24. The w is then used to diagnose the cloud droplet numbers using a simple predictive equation of cloud nucleation following previous works in the literature. Good agreement is found between diagnosed cloud droplet concentrations and predicted cloud droplet concentrations using an LES model.