Climatology of near-surface wind patterns over Switzerland

Over complex, mountainous terrain the near-surface winds can form intricate patterns as large-scale winds and locally forced wind systems interplay. S witzerland, with its mountainous topography and dense meteorological networ k of 115 automated surface stations, ideally serves as a study area for suc h wind system interactions. Applying an automated classification scheme to the wind data of one single year (1995), 16 distinct near-surface flow patt erns were found. These patterns also show characteristic distributions in m agnitude and areal extent of temperature, global radiation and precipitatio n. An Is-year climatology of flow patterns was created with an identificati on method for fewer stations. This allowed the determination of annual and diurnal variations in the frequencies of occurrence of the different flow p atterns, revealing pronounced daytime and night-time classes characterized by thermally forced winds. Transition probabilities between the flow patter ns were computed as well. The relationship between the near-surface wind pa tterns and the synoptic flow situation was investigated with a comparison w ith synoptic weather types defined for the Alpine region. The results show clear but not unequivocal interdependencies between the synoptic weather ty pe and the near-surface flow pattern. Copyright (C) 2001 Royal Meteorologic al Society.