Impact of Subgrid-Scale Orography Parameterization on the Simulation of Orographic Flows

Marc Georgelin Laboratoire d' Aérologie, Universitié Paul Sabatier, Toulouse, France

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Evelyne Richard Laboratoire d' Aérologie, Universitié Paul Sabatier, Toulouse, France

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Monique Petitdidier Centre de Recherches en Physique de l'Environnement, Saint Maur, France

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Aime Druilhet Laboratoire d' Aérologie, Université Paul Sabatier, Toulouse, France

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Abstract

A subgrid-scale orography parameterization based upon the use of an effective roughness length has been implemented in a mesobeta-scale model. The impact of such a parameterization is investigated in the framework of orographic flow simulations. Three mountain flow situations observed during the Pyrenees Experiment (PYREX) are studied. When subgrid-scale orography is accounted for, the mountain wave amplitude is reduced, the blocking is increased, the leeside low-level turbulence is intensified, and the regional wind characteristics are modified. Detailed comparisons made with the PYREX data indicate that the inclusion of subgrid orography yields a significant improvement in the model results.

Abstract

A subgrid-scale orography parameterization based upon the use of an effective roughness length has been implemented in a mesobeta-scale model. The impact of such a parameterization is investigated in the framework of orographic flow simulations. Three mountain flow situations observed during the Pyrenees Experiment (PYREX) are studied. When subgrid-scale orography is accounted for, the mountain wave amplitude is reduced, the blocking is increased, the leeside low-level turbulence is intensified, and the regional wind characteristics are modified. Detailed comparisons made with the PYREX data indicate that the inclusion of subgrid orography yields a significant improvement in the model results.

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