WRF Simulations of Upslope and Downslope Flows Over The Guadarrama Mountain Range (Spain)

The study of mesoscale circulations generated due to temperature contrasts in mountainous areas is of particular significance for various reasons: they interact with other mesoscale phenomena such as sea breezes and urban circulations (Miao et al., 2015); they can influence the diffusion of pollutants and fog formation; and they eventually alter turbulent fluxes. For instance, Sun et al. (2006) reported an anomalous positive carbon dioxide (CO2) flux just after sunset, suggesting that it was probably due to the sudden transition from upslope (anabatic) to downslope (katabatic) flow.

Micrometeorological instrumentation has recently been installed under the Guadarrama monitoring network (GuMNet, www.ucm.es/gumnet) project in La Herrería site, which is located at the foot of the Guadarrama mountain range (approximately at 900 m a.g.l.), 45 km away from the city of Madrid (Spain). This station will provide a database of great relevance for local circulations and turbulent-flux studies. Among others, it will allow to evaluate the diurnal evolution of turbulent fluxes of CO2, water vapor, momentum and heat, as well as the CO2 and energy balance in a complex-terrain region. Measurements are carried out at different levels with a sampling rate of 20 Hz in a 10m height tower and, additionally, a portable 4m height tower is available for supplementary measurements.

As a preliminary study, this work presents numerical simulations performed using the Weather Research and Forecasting (WRF) model over the aforementioned region. A period of almost stationary stable synoptical conditions is simulated in order to capture the transition from upslope to downslope flows, analyzing the evolution of the Planetary Boundary Layer (PBL) and its vertical structure. The model is tested for different PBL schemes and the topo_wind option for complex topography (Jiménez et al., 2012).

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Miao, Y., Shuhua, L., Zheng, Y., Wang, S. & Chen, B. (2015). Numerical Study of the Effects of Topography and Urbanization on the Local Atmospheric Circulations over the Beijing-Tianjin-Hebei, China. Adv Meteorol, 2015, 1-16.

Sun, H., Clark, T.L., Stull, R.B. & Black, T.A. (2006). Two-dimensional simulation of airflow and carbon dioxide transport over a forested mountain. Part I: Interactions between thermally-forced circulations. Agric For Meteorol, 140, 338-351.