The Nocturnal Wind Speed and Sensible Heat Flux over Flat Terrain

During nocturnal cooling over land, the 10-m wind speed falls to very low values in many parts of the world while the absolute sensible heat flux increases initially after sunset but reaches a maximum before decreasing later in the night. In contrast, a one-dimensional numerical model predicts that the nocturnal wind speed is constant after an initial reduction at the evening transition. The difference between observations and the model is attributed to topographic effects which can be significant even over minor orography. Using data from exceptionally flat sites, we show that, in the absence of topography, the nocturnal wind speed is constant and the sensible heat flux tends towards a limiting value during prolonged surface cooling.