MESOSCALE SURFACE-WIND CHARACTERISTICS AND POTENTIAL GRAVITY-WAVE FORMATION DURING CROSS-ALPINE AIR-FLOW

Mesoscale flow characteristics in the Alpine region are deduced from a set of daily large-scale analyses (1981-1990) by means of statistical -dynamical downscaling. This method utilizes the results of a large nu mber of mesoscale numerical simulations in combination with known stat istics of the forcing large-scale conditions. The investigation is res tricted to cross-Alpine large-scale flow from 165 to 265 degrees at 50 0 hPa. Such types of flow are favourable to south foehn. The results p rovide model-based climatological estimates of surface wind direction and upper-level gravity-wave formation at a horizontal resolution of 2 0 and 10 km. Simulated surface wind roses agree well with observations and show a dominance of low-level how around the Alps with bimodal fr equency distributions of wind direction north and south of the mountai ns. The areas where splitted hows preferably merge are identified. Gra vity waves are most likely to occur above the western parts of the Alp s. A secondary maximum of likelihood was found above Tyrol and Trentin o. Surface wind roses and gravity-wave formation are both checked with respect to their sensitivity to season (spring vs. autumn) and large- scale flow direction (south to southwest vs. southwest to west).