Simulation of banner clouds

Banner clouds are clouds in the lee of steep mountains and narrow ridges. They appear to be attached to the leeside of the mountain and flicker like a banner in the wind. Prominent examples can be found at the Zugspitze or at Mount Matterhorn (see fig. 1). The phenomenon has been known for a long time, but up to now there is no satisfying scientific explanation.

figure 1: Photograph of a banner cloud at Mount Matterhorn. The wind is blowing from right to left.

The numerical simulation of a banner cloud calls for the representation of a range of different scales and processes. The problem requires extremely powerful computing resources. The current project aims to adapt an existing Large-Eddy-Simulation model (called EULAG) to the simulation of banner clouds on the linux-cluster of the ZDV. EULAG parallelizes the code through a domain decomposition, where the different parts of the domain comminicate via MPI ('message passing interface').