Simulations of the Interactions between Shallow Cumulus Clouds and their Environment: A Lagrangian and Time Depending Perspective. (Invited)

Although we tend to summarize entrainment as simply as possible in GCMs, the processes involved are many and of turbulent nature. Using high resolution (Large Eddy) Simulations, we can resolve some of these processes, including the narrow shell of subsiding air that surrounds clouds from their environment) and see how they influence the cloud properties. To determine where mixed air originates from, or will move to, we use Lagrangian tracer particles that follow the flow. Clouds are tracked through their lifecycle to get an idea on when entrainment predominantly occurs. As it turns out, mixing over the cloud interface is overwhelmingly lateral; interactions at the cloud top can often be ignored for non precipitating cumuli. Over time however, clouds consist of several pulses, and strong fluctuations in mixing rate can be observed within these pulses.