Mechanisms and prediction of precipitation over complex terrain

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The connection between orographically influenced air flow and stratiform precipitation will be studied within the framework of the project an the basis of measured data and model simulations. Based an these results, a simplified module for nowcasting purposes of stratiform precipitation will be developed. Orographic influences and diabatic effects due to phase transformations modify the flow field in a way which is decisive for the orographically induced vertical wind field and, consequently, the intensity of orographically induced precipitation. For this reason, the analysis will first be devoted to identify the effect of flow dynamics an precipitation, such as flow over or around obstacles as well as flow blocking occurring over low mountain ranges during widespread precipitation events. The reliability with which flow fields can be represented by numerical model simulations will be investigated by data comparison. It is aimed to apply a reduced description of basic states of the flow by means of dimensionless numbers, such as Froude numbers, Rossby number or mountain aspect ratio, an the basis of measurement and simulation data. The extent to which orographic enhancement of precipitation over various mountain ranges in Europe can be expressed by these numbers is assessed. A linearized flow and precipitation model is adapted to the observed flow fields and precipitation fields over complex terrain. It will serve as a module for a new nowcasting model in the framework of the SPP 1167 Project Bundle an Nowcasting.