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The identification of katabatic flows and their characteristics observed on a simple slope (the western side of Hymettos mountain) for a six-month period (January to June, 1990) are presented. This is the first application of data obtained from an 84 m high meteorological research tower recently erected at the National Center for Scientific Research “Demokritos” in Athens, Greece. The tower is described with respect to construction and instrumentation. The topography of the region and the observational site are also described. Criteria for the identification of katabatic flows are presented, while the frequency of occurrence of such flows is estimated. Finally, two case studies are analysed in order to reveal the special characteristics of the katabatic flows.

The three-dimensional compressible non-hydrostatic mesoscale model ADREA, developed at NCSR “Demokritos” for wind field and dispersion predictions in complex terrain, is used to perform two-dimensional simulations of orographically induced precipitation. The model makes use of a simple cartesian grid by allowing blocked areas in the grid volumes and grid faces which are crossed by the irregular topography (the so-called porous-medium concept). Additionally, since we are seeking both simplicity and low computational requirements, only one prognostic equation for the whole of the water substance is implemented. The model equations are based on the theory developed for multicom-ponent/multiphase mixtures and give full account of the effects arising from the relative motion between water particles and moist air. The evaluation of the feasibility of this approach is obtained by comparing model predictions with measurements and analytical results concerning orographic precipitation episodes in the mountain barrier of Sierra Nevada.