The impact of a forest parametrization on coupled WRF-CFDsimulations during the passage of a cold front over the WINSENTtest-site

The Weather Research and Forecasting (WRF) Model has been coupled with a URANS Model to simulate the passage of a cold front over the WINSENT site, a wind energy test-site under development. It is located on a hill near a steep, forested terrain edge. A high spatial resolution is necessary to simulate the flow over this complex site accurately for which reason the WRF model is run at high resolution in LES mode coupled to a URANS model with an even higher resolution. A forest parametrization is implemented in both models to account for the drag caused by the trees. The main result is that the WRF model without forest parametrization overestimates the wind speed in the lowest 100 m above ground on average by about 3 ms−1. Introducing the forest parametrization reduces the bias considerably, but overcompensates the error at 45 m above ground, leading to a small negative bias. The URANS model further improves the flow simulation and provides a nearly bias free simulation compared to observation. Observations are taken with a 100-m high met-mast at five different levels. In addition, wind measurements taken with an Unmanned Aircraft System provide data along a cross-section that intersects the terrain edge.