On the Simulation of Subgrid Orographic Effects in Numerical Forecasting

Josef Egger Institut fuer Theoretische Meteorologie der Universitaet Muenchen

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Abstract

The primitive equations for an incompressible, homogeneous fluid confined in a channel are integrated numerically in time with a horizontal grid size of 350 km. At each time step a special integration is performed to determine the influence of a subgrid mountain with a diameter of ∼700 km located at the center of the channel. The results of a 48-hr forecast are compared with those of an integration with a smaller grid size which includes the orographic effects in the usual way. The correspondence is found to be quite satisfactory.

Abstract

The primitive equations for an incompressible, homogeneous fluid confined in a channel are integrated numerically in time with a horizontal grid size of 350 km. At each time step a special integration is performed to determine the influence of a subgrid mountain with a diameter of ∼700 km located at the center of the channel. The results of a 48-hr forecast are compared with those of an integration with a smaller grid size which includes the orographic effects in the usual way. The correspondence is found to be quite satisfactory.

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