An Operational, Diagnostic Surface Energy Budget Model

Abstract

In recent years, there has been a growing appreciation of the importance of land?atmosphere interactions in determining the state of the boundary layer. To examine this phenomenon in more detail, a new technique has been developed to evaluate the surface energy budget during the daytime from standard meteorological observations. Using only Oklahoma Mesonetwork (Mesonet) data at 5- and 30-min intervals as input, the technique calculates net radiation (Rn), ground heat flux (G), and latent heat flux (LE). The sensible heat flux (H) is calculated as a residual. The Rn term is calculated using observed values of downwelling shortwave radiation, an improved method of estimating downwelling longwave radiation, and simple parameterizations of upwelling shortwave and longwave radiation. The modeled values of Rn are unbiased and are consistently within 25 W m?2 of observed values. Ground heat flux, which is the combination of a 5-cm soil flux term and a storage term, was difficult to verify without prior knowledge of vegetation height. Latent heat flux is calculated from the Penman?Monteith equation, in which surface resistance is estimated. Using data from the Atmospheric Radiation Measurement Program, simple parameterizations were developed (one each for eastern and western Oklahoma) for this term, based on observations of temperature, relative humidity, solar radiation, soil moisture, and estimates of leaf age. Net radiation and G are calculated, and then their sum is partitioned into H and LE. Because there were no observations of LE at the Mesonet sites, the preexisting reliable estimates of H were used to verify the new estimates of both H and LE. Because there were problems with the soil moisture data from some of the sites, data from only two Mesonet sites were available for verification. The estimates of H were unbiased and within 60 W m?2 (rmse) at the sites in both eastern and western Oklahoma. Because of the limited verification data currently available, the model results are preliminary and in need of further testing.