Relation of slope winds to the ambient flow over gentle terrain

Four years of continuous tower data collected at the Risø National Laboratory are analyzed to study the climatological influence of a gentle slope on surface winds. Under very stable nocturnal conditions, the surface air tends to flow down the slope, at least intermittently, regardless of the direction of the overlying ambient wind. With more significant upslope ambient wind and only modest stability, downslope gravity flow is normally prevented. However, the slope-buoyancy effect is still of importance in that it retards the upslope flow of cold air. This effect is of climatic importance for the data studied here.