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Application of Vertical-Mode Initialization to a Limited-Area Model in Flux Form

Keith D. SashegyiScience Applications International Corporation, MeLean, Virginia

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Rangarao V. MadalaNaval Research Laboratory, Washington, D. C.

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Abstract

The vertical-mode initialization procedure of Bourke and MeGregor is applied to a limited-area weather prediction model that is formulated in flux form and is shown to be successful in reducing the undesirable gravity-wave oscillations in integrations of the numerical model. Alternative boundary conditions are developed for the scheme so that the changes to the wind at the lateral boundaries of the model are consistent with the changes in the integrated mass divergence and vorticity over the domain. The convergence of the modified scheme is shown to be rapid for two different grids. For a grid with significant topography along the lateral boundaries, use of increased diffusion in the boundary zone is shown to negatively impact the convergence of the scheme. Model integrations are performed to show the effectiveness of the scheme with improved boundary conditions in removing the gravity-wave oscillations. The results are compared with the damping of the gravity waves in the boundary zone by the time-integration scheme and by different lateral boundary treatments. The influence of noisy boundary values is also tested.

Abstract

The vertical-mode initialization procedure of Bourke and MeGregor is applied to a limited-area weather prediction model that is formulated in flux form and is shown to be successful in reducing the undesirable gravity-wave oscillations in integrations of the numerical model. Alternative boundary conditions are developed for the scheme so that the changes to the wind at the lateral boundaries of the model are consistent with the changes in the integrated mass divergence and vorticity over the domain. The convergence of the modified scheme is shown to be rapid for two different grids. For a grid with significant topography along the lateral boundaries, use of increased diffusion in the boundary zone is shown to negatively impact the convergence of the scheme. Model integrations are performed to show the effectiveness of the scheme with improved boundary conditions in removing the gravity-wave oscillations. The results are compared with the damping of the gravity waves in the boundary zone by the time-integration scheme and by different lateral boundary treatments. The influence of noisy boundary values is also tested.

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