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  • Author or Editor: Mukut B. Mathur x
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Mukut B. Mathur

Abstract

A four-level primitive equation model is integrated to 96 hr. A multiple-grid system is used to increase the resolution near the center of the hurricane. The convective and nonconvective release of latent heat, surface friction, transfer of sensible and latent heat from the sea surface to air, and the variation of Coriolis parameter with latitude are incorporated in the model.

The initial balanced state is derived from conventional and aircraft reconnaissance data over the Gulf of Mexico on 10 October 1964, defining a weak tropical depression. Results of the integration show that the model simulates fairly well the movement, the rate of intensification, the asymmetries in the wind field in the lower and the middle troposphere, and the banded structure in the vertical motion field which were observed in Isbell 1964. The temperature lapse curve at the center of the simulated hurricane lies close to the lapse curve that was observed in the eye of Isbell.

Numerical results suggest three stages in the life cycle of the simulated hurricane-formative, storm and hurricane. In the formative stage (00–48 hr), the low-level circulation becomes well marked and extends to the middle troposphere. Appreciable warming in the middle troposphere occurs. During the period 48–72 hr, the depression intensifies into a storm. Well-marked zones of convergence form in the boundary layer. Scattered bands in the vertical motion field appear in the middle and the upper troposphere and are located at considerable distance (150 km) from the center. Intense warming in the middle and the upper troposphere takes place in the hurricane stage (72–96 hr). Realistic magnitudes of the maximum surface pressure gradient (20 mb in 37 km) and the rate of intensification (21 mb during the period 84–96 hr) are simulated. Other features of hurricanes which are realistically simulated include organized bands in the vertical motion field close to and surrounding the eye, downward motion in the eye, and the cyclonic out-flow in the upper troposphere.

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Mukut B. Mathur

Abstract

The developments of the propagating and the stationary bands in a three-dimensional model of a hurricane (Isbell, 1964) are investigated. Propagating bands in the vertical motion fields in the middle and the upper troposphere form in the regions of strong heating in the upper troposphere and weak cooling in the middle troposphere. The structures of the wind, temperature and pressure fields in these bands are similar to those observed in the outer radar bands of hurricanes. Strong, nearly stationary bands form close to the center in the intense storm stage.

Results of two experiments, one (M1) in which the so-called nonconvective release of latent heat in the upper troposphere is included and the other (M2) in which this heating is not incorporated, are compared. Convective release of latent heat is included in both experiments. The stationary bands in which form in M1, also develop in M2. The propagating bands which form in M1, however, do not develop in M2. The rate of intensification of the simulated storm in M1 is nearly the same as observed in Isbell; it is, however, significantly weaker in M2. It is shown that the inclusion of nonconvective release of latent heat in M1 enhances the upper tropospheric outflow which induces strong zones of convergence in the boundary layer. The resulting increase in the upward motion at the top of the boundary layer augments the convective release of latent heat and leads to a rapid intensification of the disturbance.

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