10.4 On the Reproducibility of Surface Wind Direction Over Complex Terrain by the WRF Mesoscale Model

Jimenez, Pedro A., Centre for Energy, Environment, and Techonology (CIEMAT) and J. Dudhia, NCAR

The ability of the WRF model to reproduce the surface wind direction over complex terrain is examined. A simulation spanning a winter season is compared against wind direction records from a mesoscale network located in a complex terrain region in the Northeast of the Iberian Peninsula. A previous evaluation has shown the ability of WRF to reproduce the wind speed over the region. Hence, the present investigation complements the previous evaluation providing information of the model's ability to reproduce the direction of the surface flow. The errors are quantified in terms of scores explicitly designed to deal with the circular nature of the wind direction. Results show that the errors depend on the wind speed. The larger the wind speed the smaller the wind direction errors. Areas with more complex terrain tend to show larger errors that can present even a systematic behavior. The importance of the grid point selected for the comparison with observations is also analyzed. The wind information from the nearest grid point is not always the most adequate over areas of complex terrain where nearby grid points can provide better comparison with observations. These representativeness errors are less important over gentle terrain. A statistical correction of the simulation based on simple linear regressions is also explored. The correction suppresses the systematic errors that occur at high wind speeds providing better estimations of the wind direction.