Long-term simulation of the boundary layer flow over the double-ridge site during the Perdigão 2017 field campaign

Abstract. The Perdigão campaign 2017 was an international field campaign to measure the flow and its diurnal variation in the atmospheric boundary layer over complex terrain. A huge data set of meteorological observations was collected over the double-hill site by means of state-of-the-art meteorological measurement techniques. A focus of the campaign was the interaction of the boundary layer flow with a single wind turbine, which was located on the south-western (SW) ridge top. In this study, a long-term nested large-eddy simulation (LES) of 49-day duration with a maximum horizontal resolution of 200 m is used to describe both the general meteorological situation over Spain and Portugal and the local small-scale flow structures over the double hill during the intensive observation period (IOP). The simulations show that frequently observed nocturnal low-level jets (LLJs) from the NE have their origin over the slopes of the elevated plateau between the Portuguese Serra da Estrela and the Spanish Sierra de Gata mountain ranges N and NE of Perdigão and that the diurnal clockwise turning of the wind direction over the double ridge is induced by slope and valley winds under weak synoptic conditions. It is found that, in spite of the long simulation time, modelled and observed wind structures on the ridge tops agree well, while along-valley flow within the valley is underestimated by the model.