干旱区生态环境知识资源中心

Radiation and energy balance components are required to validate global, regional, and local scale models representing surface heat flux relationships in the heterogeneous surfaces of the world’s arid and desert regions. Research was conducted in north-eastern Nevada, U.S.A., in a Great Basin inhomogeneous semi-arid desert valley located at 40 degrees 44’ N, 114 degrees 26’ W, with an elevation of 1707 m above mean sea level, to study the daily, monthly, and annual mesoscale radiation and energy balance components. We established five radiation stations along with five Bowen ratio systems to measure the incoming (R-si) and outgoing (R-so) solar (shortwave) radiation,net (R-n) radiation, air temperatures and moisture at 1 and 2 m above-ground, the aggregated (soil + vegetation) surface temperature, soil heat flux at 8 cm (three locations at each station), soil temperatures at 2 and 6 cm above each soil flux plate, wind speed and direction at 10 m, and precipitation (if any) every 5 s averaged into 20 min throughout the valley during the 93-94 water year (beginning 1 October). Our study during the 93-94 water year showed that albedo (R-so/R-si) ranged from 85% (snow-covered surface) to 10% (cloudy skies with wet surface) among stations. The water year total incoming solar radiation (averaged among stations) amounted to 6.33 X 10(3) MJ.m(-2) and about 24% of that was reflected back to the atmosphere. The net longwave radiation (R-ln = R-lo - R-ji) was about 32% of R-si, where R-lo and R-ji are the terrestrial (outgoing) and atmospheric (incoming) longwave radiation, respectively. The 93-94 water year average net radiation (R-n) among stations amounted to 2.68 X 10(3) MJ. m(-2) (about 44% of R-si). Approximately 85.3% and 14.6% of R-n were used for the processes of sensible (H) and latent (LE) heat fluxes, respectively. The annual R, contribution to surface soil heat flux (G(surf)) was almost 0.1%. Monthly and annual relationships among radiation and energy balance components are also reported. Using just one pyranometer and these relationships, one can estimate the daily, monthly, and annual values of R80, Rn, Rln, LE, H, and G(surf). We have made a major step toward being able to estimate net radiation of heterogeneous desert landscape based on vegetation cover and irradiance levels. The results can be applied to any similar closed desert basin in Australia, the Great Basin in the U.S.A., the Middle East, and North Africa. (C) 1997 Academic Press Limited.