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Landscape-Induced Atmospheric Flow and its Parameterization in Large-Scale Numerical Models

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  • 1 Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado
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Abstract

Extensive numerical simulations are performed to demonstrate that the landscape-induced mesoscale sensible heat, moisture, and momentum fluxes associated with spatially heterogeneous convective boundary layers can be larger than, and have a different vertical structure from, the turbulent fluxes for a typical general circulation model grid box. The mesoscale fluxes above the convective boundary layer may also provide a natural mechanism for the strong coupling between the boundary layer and the free atmosphere above. The parameterizability of these memoscale and turbulent fluxes is demonstrated based on their predictability.

Nine dimensionless parameters are proposed, which combine large-scale quantities with local inhomogeneities and consider both horizontal and vertical variations. Based on these parameters, parameterization schemes for the mesoscale and turbulent sensible heat, moisture, and momentum fluxes in the convective boundary layer, and for the total (i.e., mesoscale plus turbulent) sensible heat, moisture, and momentum fluxes within and above the convective boundary layer are developed for general circulation models. The multiresponse randomized block permutation method is used to show that the parameterization algorithms are statistically valid representations with respect to the extensive numerical model-generated data. However, before these schemes can be reliably used in general circulation models, they need to be verified against comprehensive observational data, which will be available from current and near-future field experiments (e.g., the Boreal Forest Ecosystem-Atmosphere Study).

Abstract

Extensive numerical simulations are performed to demonstrate that the landscape-induced mesoscale sensible heat, moisture, and momentum fluxes associated with spatially heterogeneous convective boundary layers can be larger than, and have a different vertical structure from, the turbulent fluxes for a typical general circulation model grid box. The mesoscale fluxes above the convective boundary layer may also provide a natural mechanism for the strong coupling between the boundary layer and the free atmosphere above. The parameterizability of these memoscale and turbulent fluxes is demonstrated based on their predictability.

Nine dimensionless parameters are proposed, which combine large-scale quantities with local inhomogeneities and consider both horizontal and vertical variations. Based on these parameters, parameterization schemes for the mesoscale and turbulent sensible heat, moisture, and momentum fluxes in the convective boundary layer, and for the total (i.e., mesoscale plus turbulent) sensible heat, moisture, and momentum fluxes within and above the convective boundary layer are developed for general circulation models. The multiresponse randomized block permutation method is used to show that the parameterization algorithms are statistically valid representations with respect to the extensive numerical model-generated data. However, before these schemes can be reliably used in general circulation models, they need to be verified against comprehensive observational data, which will be available from current and near-future field experiments (e.g., the Boreal Forest Ecosystem-Atmosphere Study).

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