Development and Application of a Multi-scale Flow Field Analysis System for Complex Terrain

An accurate representation of flow in complex terrain is of major importance particularly for air quality related issues as well as wind energy. For air pollution modelling, an adequate representation of low wind speed conditions and inversions is a key aspect. Local scale models can resolve topographic effects at fine resolution of order 100 m, however their initialisation and specification of boundary conditions is challenging. Regional models may represent the synoptic and regional flow pattern by using nesting techniques but still have limited resolution. Several studies reported wind speed biases over basins and valleys with different models at katabatic conditions, particularly during winter.
This study presents a multi-scale modelling approach to represent these different scales utilizing high spatial resolution models at the local scale. To realize this, hourly regional model results based on multi-nesting techniques were used to simulate regional flow at 1 km horizontal resolution and finally to initialise a local flow model at 250 m resolution Optionally, in case of strong differences between simulated wind speed and temperature, measurements were used to adjust the initialisation of the local scale model. The focus of this study is laid on challenging winter conditions with low wind speeds and inversions.