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The Effect of Horizontal Resolution on Systematic Errors of the GLA Forecast Model

Tsing-Chang ChenDepartment of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa

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Jau-Ming ChenDepartment of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa

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James PfaendtnerLaboratory for Atmospheres, Goddard Space Flight Center, Greenbelt, Maryland

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Abstract

Systematic prediction errors of the Goddard Laboratory for Atmospheres (GLA) forecast system are reduced when the higher-resolution (2° × 2.5°) model version is used. Based on a budget analysis of the 200-mb eddy streamfunction, the improvement of stationary eddy forecasting is seen to be caused by the following mechanism: By increasing the horizontal spatial resolution of the forecast model, atmospheric diabatic heating over the three tropical continents is changed in a way that intensifies the planetary-scale divergent circulations associated with the three pairs of divergent-convergent centers over these continents. The intensified divergent circulation results in an enhancement of vorticity sources in the Northern Hemisphere. The additional vorticity is advected eastward by a stationary wave train along 30°N, thereby reducing systematic errors in the lower-resolution (4° × 5°) GLA forecast model.

Abstract

Systematic prediction errors of the Goddard Laboratory for Atmospheres (GLA) forecast system are reduced when the higher-resolution (2° × 2.5°) model version is used. Based on a budget analysis of the 200-mb eddy streamfunction, the improvement of stationary eddy forecasting is seen to be caused by the following mechanism: By increasing the horizontal spatial resolution of the forecast model, atmospheric diabatic heating over the three tropical continents is changed in a way that intensifies the planetary-scale divergent circulations associated with the three pairs of divergent-convergent centers over these continents. The intensified divergent circulation results in an enhancement of vorticity sources in the Northern Hemisphere. The additional vorticity is advected eastward by a stationary wave train along 30°N, thereby reducing systematic errors in the lower-resolution (4° × 5°) GLA forecast model.

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