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').