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- Author or Editor: STANLEY L. ROSENTHAL x
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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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Abstract
Wave solutions to the linearized, quasi-hydrostatic equations for adiabatic, nonviscous flow on an equatorially oriented beta plane are obtained. The basic current is assumed to be zonal and invariant in both space and time. Only solutions for which the meridional wind component is symmetric with respect to the equator are considered. Disturbances with wavelengths on the order of 103 km. are found to be very nearly nondivergent. The solutions show the meridional wind component to be very nearly geostrophic even at very low latitudes. The perturbation of the zonal wind, however, is highly ageostrophic at the very low latitudes and significantly ageostrophic even in subtropical latitudes.
Abstract
Wave solutions to the linearized, quasi-hydrostatic equations for adiabatic, nonviscous flow on an equatorially oriented beta plane are obtained. The basic current is assumed to be zonal and invariant in both space and time. Only solutions for which the meridional wind component is symmetric with respect to the equator are considered. Disturbances with wavelengths on the order of 103 km. are found to be very nearly nondivergent. The solutions show the meridional wind component to be very nearly geostrophic even at very low latitudes. The perturbation of the zonal wind, however, is highly ageostrophic at the very low latitudes and significantly ageostrophic even in subtropical latitudes.
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.
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.
EXPERIMENTS WITH A NUMERICAL MODEL OF TROPICAL CYCLONE DEVELOPMENT
Some Effects of Radial Resolution
Abstract
The model assumes the storm to be circularly symmetric and is expressed in z-coordinates. The information levels correspond to pressures in the mean tropical atmosphere of 1015, 900, 700, 500, 300, 200, and 100 mb. The heating function for the cyclone scale motion is simulated by a convective adjustment of the lapse rate towards a pseudoadiabat representative of ascent from the surface boundary layer. The rate of this adjustment is calibrated so that the vertically integrated heating function is related to the upward flux of water vapor through the surface boundary layer.
Experiments with 10- and 20-km radial resolution are compared. The 10-km calculation yields a storm with more realistic structure. The 20-km case does not contain a well-defined eye, whereas the 10-km experiment does. Rainfall, kinetic energy production, and efficiency are all larger with 20-km resolution. In both experiments, computational damping is an important component of the kinetic energy budget; however, the total dissipation of kinetic energy (computational plus explicit) is fairly reasonable in comparison to that found in empirical studies.
Abstract
The model assumes the storm to be circularly symmetric and is expressed in z-coordinates. The information levels correspond to pressures in the mean tropical atmosphere of 1015, 900, 700, 500, 300, 200, and 100 mb. The heating function for the cyclone scale motion is simulated by a convective adjustment of the lapse rate towards a pseudoadiabat representative of ascent from the surface boundary layer. The rate of this adjustment is calibrated so that the vertically integrated heating function is related to the upward flux of water vapor through the surface boundary layer.
Experiments with 10- and 20-km radial resolution are compared. The 10-km calculation yields a storm with more realistic structure. The 20-km case does not contain a well-defined eye, whereas the 10-km experiment does. Rainfall, kinetic energy production, and efficiency are all larger with 20-km resolution. In both experiments, computational damping is an important component of the kinetic energy budget; however, the total dissipation of kinetic energy (computational plus explicit) is fairly reasonable in comparison to that found in empirical studies.
