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An Examination of Frontal Structure in a Fine–Primitive Equation Model for Numerical Weather Prediction

Daniel KeyserNational Center for Atmospheric Research, Boulder, CO 80307

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Melvyn A. ShapiroNational Center for Atmospheric Research, Boulder, CO 80307

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Donald J. PerkeyNational Center for Atmospheric Research, Boulder, CO 80307

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Abstract

The structure of upper level and surface frontal zones associated with a cyclone developing over the central United States on 21–22 February 1971, as predicted by a limited-area, moist, primitive equation model with horizontal and vertical grid spacing on the order of 100 and 1.5 km, respectively, Is qualitatively examined and discussed. A comparison of crow-section analyses of the frontal zones, constructed from rawinsondo observations and from model output data, reveals that the horizontal and vertical scales of the observed fronts are ∼100 and ∼1 km, while those for the model-predicted fronts are ∼200–400 and ∼1–2 km. The discrepancy in scale can be explained by the coarse model resolution, which essentially renders be frontal zones subgrid-scale phenomena. Despite the model's lack of fidelity in reproduce the observed details in frontal structure, point calculations with Miller' equation appear reasonable in view of those results obtained in previous synoptic investigations. Vertical tilting dominates the frontolysis predicted in the upper level frontal exit region, and the stretching deformation term provides a strong frontogenetical contribution in the surface frontal zone.

Abstract

The structure of upper level and surface frontal zones associated with a cyclone developing over the central United States on 21–22 February 1971, as predicted by a limited-area, moist, primitive equation model with horizontal and vertical grid spacing on the order of 100 and 1.5 km, respectively, Is qualitatively examined and discussed. A comparison of crow-section analyses of the frontal zones, constructed from rawinsondo observations and from model output data, reveals that the horizontal and vertical scales of the observed fronts are ∼100 and ∼1 km, while those for the model-predicted fronts are ∼200–400 and ∼1–2 km. The discrepancy in scale can be explained by the coarse model resolution, which essentially renders be frontal zones subgrid-scale phenomena. Despite the model's lack of fidelity in reproduce the observed details in frontal structure, point calculations with Miller' equation appear reasonable in view of those results obtained in previous synoptic investigations. Vertical tilting dominates the frontolysis predicted in the upper level frontal exit region, and the stretching deformation term provides a strong frontogenetical contribution in the surface frontal zone.

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