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United States Department of Agriculture

Agricultural Research Service

Title: Implications of Radiometric-Aerodynamic Temperature Differences for Heat Flux Estimation

Authors
item KUSTAS, WILLIAM
item ANDERSON, MARTHA
item Norman, John - UNIV. OF WI

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2006
Publication Date: June 1, 2006
Citation: Kustas, W.P., Anderson, M.C., Norman, J.M. 2006. Implications of radiometric-aerodynamic temperature differences for heat flux estimation [abstract]. EOS Transactions, American Geophysical Union, Joint Assembly Supplements, 87(36). Paper No. H23F-01.

Technical Abstract: In the application of radiometric surface temperature observations for heat flux computations in numerical models, it is necessary to consider differences between the so-called “aerodynamic” temperature, which is the model-derived temperature that relates to the efficiency of heat exchange between the land surface and overlying atmosphere, and a “surface” temperature measurement from a thermal-infrared radiometer, which largely corresponds to a weighted soil and canopy temperature as a function of radiometer viewing angle. A number of studies over the past several years using multi-source canopy models and/or experimental data have developed simplified methods to accommodate radiometric-aerodynamic temperature differences. In this study, simulations by a detailed multi-source soil-plant-environment model, Cupid, which considers both radiative and turbulent exchanges across the soil-canopy-air interface, are used to explore the radiometric-aerodynamic temperature relations for a semi-arid shrubland ecosystem under a range of leaf area/canopy cover, soil moisture and meteorological conditions. The simulated radiometric-aerodynamic temperatures indicate that leaf area or vegetation density strongly affects the magnitude of this temperature difference; however the relationships are non-unique, having significant variability depending on local conditions. These simulations also show that soil-canopy temperature differences are highly correlated with variations in the radiometric-aerodynamic temperature differences, with the slope being primarily a function of leaf area. This result suggests that land surface models which explicitly parameterize radiative and convective exchanges from the soil and vegetation components (two-source) may be better able to accommodate variability in the radiometric-aerodynamic relation for a wider range in vegetated canopy cover conditions. Comparisons of sensible heat flux estimates from a simplified two-source model scheme and the standard bulk or one-source land surface model approach with Cupid simulated output as well as experimental observations will be presented.

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