Approaches for Averaging Surface Parameters and Fluxes over Heterogeneous Terrain

A. Chehbouni Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California

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E. G. Njoku Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California

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J-P. Lhomme ORSTOM, Hydrology Laboratory, Montpellier, France

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Y. H. Kerr CESBIO/CNES, Toulouse, France

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Abstract

Successful prediction of possible climate change depends on realistic parameterization of land surface processes in climate models. Such parameterizations must take appropriate account of the heterogeneities that are found in most earth surfaces. In this study, different average strategies for aggregating patch-scale heterogeneities to scales that are appropriate for mesoscale and climate model gods have been explored. A simple model for estimating area-average “effective” surface flux parameters is evaluated. The model satisfies the energy balance equation and leads to a set of relationships between local and effective parameters in the governing equations for the surface energy balance. One outcome is that the resulting effective surface temperature is not a simple area-weighted average of component temperatures, but is a function of a specific combination of different resistance of the individual surface elements. A set of heterogeneous surfaces has been simulated to study the effective fluxes obtained using the described model. A comparison with results obtained by other investigators using different averaging methods is also performed.

Abstract

Successful prediction of possible climate change depends on realistic parameterization of land surface processes in climate models. Such parameterizations must take appropriate account of the heterogeneities that are found in most earth surfaces. In this study, different average strategies for aggregating patch-scale heterogeneities to scales that are appropriate for mesoscale and climate model gods have been explored. A simple model for estimating area-average “effective” surface flux parameters is evaluated. The model satisfies the energy balance equation and leads to a set of relationships between local and effective parameters in the governing equations for the surface energy balance. One outcome is that the resulting effective surface temperature is not a simple area-weighted average of component temperatures, but is a function of a specific combination of different resistance of the individual surface elements. A set of heterogeneous surfaces has been simulated to study the effective fluxes obtained using the described model. A comparison with results obtained by other investigators using different averaging methods is also performed.

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