A Quasi-Geostrophic Numerical Model Incorporating Effects of Release of Latent Heat

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  • 1 Meteorological Service of Canada, Toronto
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Abstract

A quasi-geostrophic numerical model for predicting precipitation amounts and the heights of the 1000-, 850-, 700-, 500-, and 300-mb surfaces is described. The basic equations are the vorticity and omega equations. Influences of released latent heat are incorporated in the static stability in the latter equation. Frictional and orographic effects are included in the lower boundary condition for the vertical velocity.

Numerical integrations are carried out for 36 hours in a case of intense cyclogenesis over central United States. “Moist” and “dry” predictions are made, the latter by artificially excluding effects of release of latent heat. In the “dry” prognosis, the sea-level low is moved northeastward but not intensified. By contrast, in the “moist” prediction it is rapidly deepened. Forecast precipitation amounts agree roughly in magnitude with observations. However, the occurrence of heavy convective precipitation along the cold front is not satisfactorily predicted.

Abstract

A quasi-geostrophic numerical model for predicting precipitation amounts and the heights of the 1000-, 850-, 700-, 500-, and 300-mb surfaces is described. The basic equations are the vorticity and omega equations. Influences of released latent heat are incorporated in the static stability in the latter equation. Frictional and orographic effects are included in the lower boundary condition for the vertical velocity.

Numerical integrations are carried out for 36 hours in a case of intense cyclogenesis over central United States. “Moist” and “dry” predictions are made, the latter by artificially excluding effects of release of latent heat. In the “dry” prognosis, the sea-level low is moved northeastward but not intensified. By contrast, in the “moist” prediction it is rapidly deepened. Forecast precipitation amounts agree roughly in magnitude with observations. However, the occurrence of heavy convective precipitation along the cold front is not satisfactorily predicted.

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