Investigation of physical mechanisms leading to cell broadening and organization of convection in cold air outbreaks utilizing high resolution LES model simulations
Responsible: Heiko Jansen
Project type: individual ​DFG research project
Duration: 01/10/2003 - 31/01/2006

This project is concerned with the organization of convection structures triggered by so called cold air outbreaks (COA), in which cold air from the continent or sea ice areas drifts above relatively warm water. The large gradient in temperature leads to convection, which at first manifests itself by the creation of horizontal rolls. With increasing distance from the coast, the structure at some point changes to hexagonal cells. The corresponding cloud clusters are readily visible in satellite pictures.

Although research for some decades in this field, numerous open questions remain. For example, the aspect ratio of the cells, defined as the ratio of their diameter to their height, cannot be simulated in models as it is observed. In reality, this ratio attains values between 10 and 30, while in models or in laboratory experiments, values of 3-4 are seen. Furthermore, it is unclear, why sometimes open cells (with downwind areas in the inner part of the cell) and sometimes closed cells (upwinds in the inner part) are observed. The origin of the cloud streets close to the coast is not known, either.

Such questions are addressed using the high resolution, massively parallel LES model PALM.