Estimation of Surface Radiation and Energy Flux Densities from Single-Level Weather Data

A scheme is proposed that relates surface flux densities of sensible heat, latent heat, and momentum to routine weather data. The scheme contains parameterizations concerning the radiation components and the surface energy flux densities. The parameteriations are developed and examined using observations from 1987 of a grass-covered surface at Cabauw in the Netherlands. It is shown that improvements in the parameterizations are achieved by incorporating an albedo dependence on solar elevation, a longwave downward radiation with a correction for the amount of high clouds, and a soil heat flux with a soil temperature approximated by a 24-h-mean 2-m temperature. In addition, the Penman-Monteith concept for the latent heat flux is utilized with a simple one-parameter surface resistance, which depends on atmospheric moisture deficit in particular. Special attention is paid to the treatment of surface inhomogeneities. A distinction is made between stable conditions, when measurements in the lower 10m appear to be in equilibrium with the local surface and unstable conditions, when measurements seem to be influenced by deviating upstream surface conditions. A constant oughness length for heat abaove grassland of 1 mm is applied. Finally, the scheme as a whole is evaluated and compared with a previous approach by A.P. van Ulden and A.A.M. Holtslag. It appears that in particular the sensible heat flux is improved with the new scheme. This can be ascribed mostly to the replacement of the modified Priestley-Taylor by the Penman -Monteith formulation and by a better presentation of the surface temperature.