A Simple Scheme for Daytime Estimates of the Surface Fluxes from Routine Weather Data

A. A. M. Holtslag Royal Netherlands Meteorological Institute, De Bilt, The Netherlands

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A. P. Van Ulden Royal Netherlands Meteorological Institute, De Bilt, The Netherlands

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Abstract

In this paper a simple empirical scheme is presented, which gives hourly estimates of the surface fluxes of heat and momentum from routine weather data during daytime. The scheme is designed for grass surfaces, but it contains parameters which take account of the surface properties in general. The required input weather data are no more than a single wind speed, air temperature at screen height and total cloud cover. The output of the scheme is in terms of the Monin-Obukhov similarity parameters; it is obtained by using estimates for the mean values of the surface radiation and energy budget. For the climate of the Netherlands good agreement is found between a full year of observations and estimates made with the scheme. For all data it appears that root-mean-square errors are σ = 90 W m−2 for the incoming solar radiation, σ = 63 W m−2 for the net radiation, σ = 34 W m−2 for the sensible heat flux, σ = 0.01 m s−1 for the friction velocity and σ = 0.67 × 10−3 for the similarity ratio between the surface roughness length and the Obukhov stability parameter. A discussion is given an the surface parameters and coefficients of the scheme.

Abstract

In this paper a simple empirical scheme is presented, which gives hourly estimates of the surface fluxes of heat and momentum from routine weather data during daytime. The scheme is designed for grass surfaces, but it contains parameters which take account of the surface properties in general. The required input weather data are no more than a single wind speed, air temperature at screen height and total cloud cover. The output of the scheme is in terms of the Monin-Obukhov similarity parameters; it is obtained by using estimates for the mean values of the surface radiation and energy budget. For the climate of the Netherlands good agreement is found between a full year of observations and estimates made with the scheme. For all data it appears that root-mean-square errors are σ = 90 W m−2 for the incoming solar radiation, σ = 63 W m−2 for the net radiation, σ = 34 W m−2 for the sensible heat flux, σ = 0.01 m s−1 for the friction velocity and σ = 0.67 × 10−3 for the similarity ratio between the surface roughness length and the Obukhov stability parameter. A discussion is given an the surface parameters and coefficients of the scheme.

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