Simulation of Surface Fluxes and Boundary Layer Development over the Pine Forest in HAPEX-MOBILHY

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

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M. Ek Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon

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Abstract

The interaction of the atmospheric boundary layer with the heterogeneous pine forest in HAPEX-MOBILHY on a scale of order 10 km is studied. A state-of-the-art, coupled atmosphere-soil-vegetation model is used and is run for 16 June 1986 in a stand-alone mode using prescribed dynamics. Published values for the effective roughness lengths of heat and momentum from different origins are used to show the impact on the surface fluxes and the boundary layer development. The modal simulations indicate that the coupled atmosphere-vegetation system is rather sensitive to the value for the roughness length of heat. This affects in particular the sensible heat flux and, as a consequence, the boundary layer height and profiles of mean quantities in the boundary layer. The model results are compared with observations made at a forest town, with radiosonde profiles, and with aircraft data. The best overall agreement for the boundary layer quantities is obtained by using a roughness length of heat that is three orders of magnitude smaller than the roughness length of momentum.

Abstract

The interaction of the atmospheric boundary layer with the heterogeneous pine forest in HAPEX-MOBILHY on a scale of order 10 km is studied. A state-of-the-art, coupled atmosphere-soil-vegetation model is used and is run for 16 June 1986 in a stand-alone mode using prescribed dynamics. Published values for the effective roughness lengths of heat and momentum from different origins are used to show the impact on the surface fluxes and the boundary layer development. The modal simulations indicate that the coupled atmosphere-vegetation system is rather sensitive to the value for the roughness length of heat. This affects in particular the sensible heat flux and, as a consequence, the boundary layer height and profiles of mean quantities in the boundary layer. The model results are compared with observations made at a forest town, with radiosonde profiles, and with aircraft data. The best overall agreement for the boundary layer quantities is obtained by using a roughness length of heat that is three orders of magnitude smaller than the roughness length of momentum.

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