Radiometrically determined skin temperature and scalar roughness to estimate surface heat flux part II: Performance of parameterized scalar roughness for the determination of sensible heat |
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| Authors: | Michiaki Sugita Akihiro Kubota |
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| Institution: | (1) Environmental Research Center, University of Tsukuba, 305 Tsukuba, Ibaraki, Japan;(2) College of Natural Sciences, University of Tsukuba, 305 Tsukuba, Ibaraki, Japan |
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| Abstract: | Several formulations and proposals to determine the value of the radiometric scalar roughness for sensible heatz
0h,r
are tested with respect to their performance in the estimation of the sensible heat flux by means of the profile equations derived from Monin-Obukhov similarity theory. The equations are applied to the data set of spatially averaged surface skin temperature and profiles of wind speed and temperature observed in a pasture field during a growing season. The use of a physical model developed for a dense canopy to estimate scalar roughness for sensible heatz
0h,r
produced sensible heat fluxH with a correlation coefficientr=0.884, the ratio of means being  H
s
 /H=1.19 in a comparison with reference values ofH
s
. In comparison, a proposal for a fixed value ofz
0h
yieldedr=0.887, H
s
/H=0.879. In both cases, the validity ofz
0h
=z
0h,r
was assumed. All expressions derived to estimatez
0h,r
from a multiple linear regression with such predictors as leaf area index, solar radiation and the ratio of solar radiation to extraterrestrial radiation, were found to produce a better result, withr better than 0.90 and H
s
/H around 1.0. However, when the constantsc andf of a linear regression equationHs=cH+f are used to evaluate the equations, a marked difference in performance of each formulation appeared. In general, equations with smaller numbers of predictors tend to produce a biased result, i.e., an overestimation ofH at largeH
s
. These values ofH are used in conjunction with the energy balance equation to derive values of the latent heat fluxLE, which are shown to be in good agreement with the reference valuesLE
s
, withr greater than 0.97. |
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| Keywords: | |
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