Cloud Physics and Modeling

soatlantic-a2002157-1055-1km

Image from visibleearth.nasa.gov

cloud_particles

Image from arm.gov

Cloud physics (or microphysics) is the study of the formation and evolution of (small) cloud droplets and (large) precipitation particles. Cloud dynamics is the study of the turbulent processes by which clouds form, grow, and mix with surrounding air until they evaporate.

Neither cloud physical nor cloud dynamical processes can be fully resolved by present-day weather forecast or climate models. That means that we humans have to (get to!) use our ingenuity in order to estimate the effects of clouds on the simulated atmosphere. Not every phenomenon can be left to the supercomputers.

Many fundamental questions remain unsolved in the areas of cloud physics and cloud dynamics. For instance, the set of mechanisms by which ice crystals form in the atmosphere has not been fully mapped out. (Cloud droplets do not spontaneously freeze at -1 C!) To cite another example, quasi-hexagonal rings of clouds sometimes form over the oceans, and the reasons are still somewhat mysterious.

Led by Prof. Vince Larson, researchers at UWM have co-developed a cloud parameterization, “CLUBB,” that estimates the effects of small-scale clouds in coarse-resolution models. It is a unified parameterization that strives to parameterize all cloud types – including stratiform, shallow cumulus, and deep cumulus – using a single equation set. CLUBB has been implemented in a leading climate model, the Community Atmosphere Model (CAM). This model is freely available to students who wish to explore hypotheses regarding cloud and microphysical processes.