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Stanley L. Rosenthal

Abstract

Numerical experiments with an axisymmetric model of the tropical cyclone are described. The model contains a cumulus parameterization of the type proposed by Ooyama (1971). It is shown that the growth of the hurricane scale is significantly affected when the cloud model and the form of the cloud spectrum are altered. The growth of the hurricane is also strongly affected by the manner in which resolvable supersaturation is treated.

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Stanley L. Rosenthal

Abstract

A set of regression equations, which relate the 05, 25, 50, 75, and 95 per cent points of the surface-air temperature frequenry distributions over the North Atlantic Ocean to mean temperatures interpolated from charts contained in the U. S. Navy Marine Climatic Atlas of the World, Vol. I, North Atlantic Ocean, is obtained. With these equations and the previously mentioned climatic atlas, one can estimate the surface-air temperature frequency distribution at any given point over the North Atlantic Ocean. Tests conducted with independent data indicate that the equations give accurate results.

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Stanley L. Rosenthal

Abstract

This paper gives the results of an investigation of the interdiurnal variability of surface-air temperature at 9 of the North Atlantic Ocean Vessel Stations. Computations were performed for each month of the year over a four-year study period. Several aspects of the computational results are discussed in relation to the analogous statistics at land stations.

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Stanley L. Rosenthal

Abstract

Frequency distributions of aperiodic diurnal ranges of temperatures at 9 of the North Atlantic Ocean Vessel Stations are examined. It is found that the means, disperions, and asymmetries of these distributions are largest in winter and smallest in summer. It is also found that the aperiodic diurnal range exceeds the periodic diurnal range on virtually all winter days and on the great majority of summer days.

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Stanley L. Rosenthal

Abstract

Power spectra, covering a range of periods of from 1.2 to 30 days, of the zonal- and meridional-wind components at the 5000- and 40,000-ft levels at seven low latitude stations are presented. A brief discussion of the spectra is given.

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Stanley L. Rosenthal

Abstract

If the perturbation of the zonal wind component and the Coriolis term which arises in the zonal equation of motion as a result of vertical motions are neglected, the linearized vorticity equation and the continuity equation (when written in pressure coordinates) become a complete set for the meridional wind and vertical motion perturbations. This set is solved for a class of easterly waves which reach their maximum intensity at the equator and dampen poleward.

The theoretical streamlines and the theoretical field of divergence both agree quite well with their empirical counterparts. On the other hand, the theoretical isotachs are somewhat distorted and the theoretical phase speed is a bit low.

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Stanley L. Rosenthal

Abstract

Axisymmetric hurricane simulators with a hydrostatic model, in which the release of latent heat occurs totally in convective elements that are explicitly resolved on a 20 km horizontal grid, are presented. It is shown that there is good reason to believe that the failures of earlier attempts in this direction were due to model and experimental design. A fairly complete description of the model is given. The solutions do not depend upon overly large lateral mixing coefficients nor upon artificial numerical smoothing procedures. The relationship between this work and CISK theories of hurricane development is discussed. The impact of this work on cumulus parameterization studies is also discussed.

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STANLEY L. ROSENTHAL

Abstract

The tropical cyclone model described in previous reports is extended to include an explicit water vapor cycle. Results of experiments that examine effects due to initial humidity conditions, radial resolution, and the finite-difference scheme are discussed. Growth to the mature stage is more rapid in the moist environment, but peak intensity is not strongly affected by the initial moisture content. Rainfall rates are quite reasonable, and nonconvective precipitation is found to be a significant proportion of the total rainfall, in agreement with recent empirical results. Experiments with upstream differencing yield more realistic solutions than do experiments with centered differences. This surprising result is discussed in detail.

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STANLEY L. ROSENTHAL

Abstract

Tropical cyclone model experiments are summarized in which the drag coefficient and the analogous exchange coefficients for sensible and latent heat are varied. During the early portions of the immature stage, the response of the model storm follows linear theory and growth is more rapid with larger drag coefficients. However, the ultimate intensity reached by model storms varies inversely with the drag coefficient. The experiments indicate that air-sea exchanges of latent heat are crucial for the development and maintenance of the model storm. The air-sea exchange of sensible heat appears to be far less important.

Experiments conducted with open lateral boundary conditions revealed that the structure and intensity of the mature stage of the model cyclone is relatively insensitive to the initial perturbation and to the size of the computational domain. The time required to reach the mature stage is, however, quite sensitive to these influences.

Comparisons between experiments with open and mechanically closed lateral boundaries show the lateral boundary conditions to be extremely important. For computational domains of 2000 km or less, model cyclones with closed lateral boundaries are less intense than their counterparts with open lateral boundaries. However, the intensity of the closed systems increases markedly with domain size and the experiments suggest that differences due to boundary conditions might be minimized if the domain size exceeded 2000 km.

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STANLEY L. ROSENTHAL

Abstract

Simulations of the natural (unmodified) evolution of tropical cyclones with a circularly symmetric model suggest that seeding of hurricanes with silver iodide at radii greater than that of the surface wind maximum might be more effective in decreasing the surface wind maximum than seedings at or within the wind maximum. Seeding simulations with the model strongly suggest that the model storm responds in the sense anticipated. On the other hand, simulated seedings at radii less than that of the surface wind maximum produce temporary increases in the strength of the maximum. However, termination of the seeding is followed by a rapid recovery of the modified storm to a state close to that of the control.

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