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The model results show a complex interaction between the synoptic weather situation and local wind systems which develop in the complex Swiss terrain. In the afternoon of 29 July (Figure 10) the model shows prevailing synoptic westerly winds at lower elevation, and on the mountain tops. Elsewhere the synoptic wind is modified by local wind systems, such as lake wind systems, channeling effects in valleys, up-valley wind systems, which transport air masses from the Plateau up to the mountain regions, and up-slope wind systems on the larger mountain slopes.
The modeled wind speed (Figure 11), and wind direction (Figure 12) were compared with time series from six weather stations spread over the whole domain. The stations Suhr, Haerkingen, Aarau, and Dübendorf are all situated on the Swiss Plateau and are dominated by the synoptic wind and the SW-NE channeling between the Alps and the Jura mountains. During the afternoon, when vertical mixing is most effective, a clear wind maximum is observed. Thun is situated in a valley and is mainly influenced by local wind systems. Both synoptic and local wind regimes are influencing the elevated stations of Rigi, Enges, and Sursee.
All these wind systems are generally well reproduced by Metphomod . The model, however, sometimes has problems to properly predict if local or synoptic wind is dominant in a certain situation. In Thun, the model predicts a lake wind system during daytime on the 29 and 30 July, which in reality was only observed on the 30. It also has a tendency to predict slightly too high wind speeds, especially during the night and near the model borders (e.g. at Enges). This may be due to the fact, that the model has some difficulties to represent the situation at the ground. (The center of the lowest model layer is 25 m above the ground.)
