Simple estimates of nighttime surface fluxes from routine weather data

This report deals with hourly estimates of the surface fluxes of heat and momentum from routine weather data during nighttime. For this purpose one year of measured profiles of wind and temperature are analysed. With the measured profiles the friction velocity (u) and the temperature scale (0) are computed using the flux-profile relations of Dyer (1974). It appears that 0  decreases for very high and low windspeeds. But in an intermediate region of u it follows that  0 decreases mainly with increasing total cloud cover (N).
These results are consistent with the analysis by Venkatram (1980), which is based on the Prairie Grass, Kansas and Minnesota data. The behaviour of 0* with u and N is described. This Implies that the surface fluxes can be obtained from a single windspeed, the surface roughness length, total cloud cover and the air temperature. The required procedures are fairly simple and are described in the paper. It is shown that the proposed scheme can furnish good estimates for the flux of sensible heat, the flux of momentum in terms of the friction velocity and the Obukhov stability parameter. With the scheme a satisfactory description can be given of the nocturnal surface layer.