Testing the capability of the WRF model on representing temperature inversions in alpine basins and valleys

Persistent inversions and associated low wind situations during the winter months often lead to air pollution problems in alpine basins and valleys, regardless of emission levels. The aim of this work is to determine how well high-resolution simulations with the Weather Research and Forecasting (WRF) model are able to reproduce the occurrence and weather conditions during temperature inversions in complex topography.

The city of Graz in south-eastern Austria often experiences increased strength and persistence of winter inversions due to its location and local topography. Experiments in this area with the WRF model show a better reproduction of these weather conditions when the shortwave radiation scheme Dudhia is used instead of the RRTMG, while variations in the microphysics and planetary boundary schemes did not lead to relevant changes in the model results.

In a next step, additional basins and alpine valleys will be investigated to determine the influence of shape and extent of the topography on the results.

The model is forced with the ECMWF-IFS analysis data with a spatial resolution of 9 km. Two one-way nested domains with resolutions of 3 and 1 km are used to investigate what resolution is required to adequately represent the local topographic effects. The model results are compared with station and radiosonde observations as well as with the analysis and nowcasting system INCA for Austria.