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PRELIMINARY RESULTS FROM AN ASYMMETRIC MODEL OF THE TROPICAL CYCLONE

RICHARD A. ANTHESNational Hurricane Research Laboratory, Environmental Research Laboratories, NOAA, Miami, Fla.

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STANLEY L. ROSENTHALNational Hurricane Research Laboratory, Environmental Research Laboratories, NOAA, Miami, Fla.

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JAMES W. TROUTNational Hurricane Research Laboratory, Environmental Research Laboratories, NOAA, Miami, Fla.

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Abstract

A three-layer primitive equation model of an isolated stationary tropical cyclone is constructed. The major difference between this and previously published models is the elimination of the assumption of circular symmetry. The release of latent heat by organized cumulus convection is parameterized by use of techniques previously shown to give realistic results in symmetrical models. In particular, the total release of heat in a vertical column is given by the horizontal convergence of water vapor in the Ekman layer and the vertical distribution of the heating follows the proposals made by Kuo. In the preliminary calculation reported on here, water vapor content is not forecast but, rather, is treated implicitly as was the ease for the earlier circularly symmetric models.

The results show that the model reproduces many observed features of the three-dimensional tropical cyclone. Realistic portrayals of spiral rainbands and the strongly asymmetric structure of the outflow layer are obtained. The kinetic energy budget of the model compares favorably with empirical estimates and also shows the loss of kinetic energy due to truncation errors to be very small.

Large-scale horizontal asymmetries in the outflow are found to play a significant role in the radial transport of vorticity during the mature stage and are of the same magnitude as the transport by the mean circulation.

In agreement with empirical studies, the outflow layer of the model storm shows substantial areas of negative absolute vorticity and anomalous winds.

Abstract

A three-layer primitive equation model of an isolated stationary tropical cyclone is constructed. The major difference between this and previously published models is the elimination of the assumption of circular symmetry. The release of latent heat by organized cumulus convection is parameterized by use of techniques previously shown to give realistic results in symmetrical models. In particular, the total release of heat in a vertical column is given by the horizontal convergence of water vapor in the Ekman layer and the vertical distribution of the heating follows the proposals made by Kuo. In the preliminary calculation reported on here, water vapor content is not forecast but, rather, is treated implicitly as was the ease for the earlier circularly symmetric models.

The results show that the model reproduces many observed features of the three-dimensional tropical cyclone. Realistic portrayals of spiral rainbands and the strongly asymmetric structure of the outflow layer are obtained. The kinetic energy budget of the model compares favorably with empirical estimates and also shows the loss of kinetic energy due to truncation errors to be very small.

Large-scale horizontal asymmetries in the outflow are found to play a significant role in the radial transport of vorticity during the mature stage and are of the same magnitude as the transport by the mean circulation.

In agreement with empirical studies, the outflow layer of the model storm shows substantial areas of negative absolute vorticity and anomalous winds.

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