Cloud-wave coupling

Group Leader: Claudia Stephan

The cloud-wave coupling group studies feedbacks between convection and small-scale atmospheric waves, in particular gravity waves, to understand their role in shaping patterns of clouds and precipitating convection. Interactions between waves and convection are not well represented in contemporary climate models and could contribute to the disconcerting diversity of climate models at simulating tropical convection.

Convective sources often excite a discrete wave spectrum. Yet, gravity waves can propagate over large distances and interfere with each other. The spectral composition of the wave background and its effects on cloud statistics is not well understood. One of our scientific goals is a systematic assessment of the ambient tropospheric wave background.

We are interested in shallow as well as deep convection. In particular, we aim to understand how much of their structure shallow cumulus clouds owe to the existence of other clouds. Our group studies the spatial and temporal evolution of convective cells in a multi-cellular environment, which is partly governed by the coupling between convective cells and wave modes in the boundary layer and the free troposphere.
Another topic of interest is convective organization. The heating released by deep convection is strong enough to organize surrounding convection. Shallow and deep ducted gravity waves can promote the growth of shallow convection into long-lived convective bands. We identify events of organized convection to investigate how wave-mediated perturbations contributed to their organization.
We use satellite and radar observations to resolve the lifecycle of clouds as well as in situ measurements that are analyzed for the presence of gravity waves. Our research relies heavily on numerical experiments using a hierarchy of models. These include cloud-resolving simulations of ICON as well as several idealized configurations of the model to isolate or exclude physical processes. These targeted experiments let us identify wave sources and isolate waves to study their propagation and interaction with their environment at the process level.