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STANLEY L. ROSENTHAL and WERNER A. BAUM

Abstract

Data from the Ocean Vessel Stations have been used to determine for each month (1) the daily variations of mean surface pressure, (2) the 3-hour mean-pressure tendencies, and (3) the phases and amplitudes of the first three harmonics of the daily variations. Some implications of the results are discussed briefly.

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STANLEY L. ROSENTHAL and ROBERT W. REEVES

Abstract

The relationship between wind and pressure in the equatorial zone of a barotropic, nondivergent atmosphere is examined. Cyclostrophic effects prove to be of major importance. The results indicate that it is extremely difficult to devise pictorial models of the wind-pressure relationship near the equator. The impact of this conclusion upon operational low-latitude analysis by both subjective and machine methods is discussed.

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STANLEY L. ROSENTHAL and WALTER J. KOSS

Abstract

As a precursor to numerical simulation of tropical cyclones with multilevel vertical resolution, a linear model in which the thermodynamic equation is applied at two levels is considered. Eigenvalue solutions for conditional and unconditional heating are compared.

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HARRY F. HAWKINS and STANLEY L. ROSENTHAL

Abstract

In most tropical regions, the large-scale flow patterns are most reliably established by analysis of the wind reports. In these regions, stream functions must be calculated either wholly or partially from the wind analysis itself. To do this, however, it is necessary to specify the stream function, or its normal derivative, on the boundary of the region considered. This paper examines several schemes which may be useful for this purpose.

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RICHARD A. ANTHES, STANLEY L. ROSENTHAL, and JAMES W. TROUT

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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RICHARD A. ANTHES, JAMES W. TROUT, and STANLEY L. ROSENTHAL

Abstract

Results from a three-layer asymmetric hurricane model previously described by the authors are compared with results from an axially symmetric analog to investigate the effect of the symmetry assumption on the internal dynamics of model cyclones. The symmetric model storm initially develops more rapidly than the asymmetric storm. The differences in intensity during the first 100 hr are related to differences in horizontal resolution produced by the staggered grid used with the symmetric model. The symmetric model, on the other hand, does not produce the second period of intensification that starts at 120 hr in the asymmetric model. This fact supports the conclusion reached in the earlier paper that the development of large-scale asymmetries at 100 hr is closely related to the subsequent intensification.

Although the life cycles of the two storms are different, the azimuthally averaged structure of the asymmetric storm at maximum intensity is similar to the corresponding structure of the symmetric model storm and supports the adequacy of symmetric models in investigating many aspects of tropical cyclone structure.

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