期刊名称：Tellus A: Dynamic Meteorology and Oceanography
电子版ISSN：1600-0870
出版年度：2002
卷号：54
期号：4
页码：330-337
DOI：10.3402/tellusa.v54i4.12149
摘要：The present case study evaluates the downward longwave radiation at the surface (DLR) inseveral high-resolution (=1°) general circulation models (GCMs) using surface observationsfrom a semiarid continental site in New South Wales, Australia (Uardry, 34.39°S, 142.30°E).This site is located on a large grassland plain uniform in both its land use and landcover type,and is therefore particularly well suited for a comparison with GCM grid mean values. Monthlyaverages of newly constructed clear-sky and all-sky DLR climatologies and the resulting cloudradiativeforcing are compared. It is shown that the GCMs exceed the observed DLR undercloud-free conditions by 10–20Wm −2 at this semiarid site on an annual basis, with a strongseasonal dependence. The calculated clear-sky fluxes are overestimated during the warmersummer season, with large absolute values of DLR, while the biases are reduced in the colderand dryer winter season with smaller fluxes. This gives direct support for recent evidence thatthe DLR model biases depend systematically on the thermal and humidity structure of thecloudless atmosphere. Fluxes from strongly emitting atmospheres tend to be overestimated, butmay be underestimated from atmospheres with smaller emission. This points to common problemsinherent in the simulation of the emission from the cloudless atmosphere in current longwaveradiation codes.The comparisons of the all-sky climatologies at Uardry show that the clear-sky biases arepartly masked in the models with an insufficient cloud-radiative forcing, thereby counterbalancingthe excessive DLR of the cloud-free atmosphere. On the other hand, when the cloudradiativeforcing is improved, the biases in the cloud-free atmosphere become fully apparent inthe all-sky fluxes.
