A Numerical Study of the Interactions between Two Tropical Cyclones

Simon Wei-Jen Chang Science Applications, Inc., McLean, VA 22102

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Abstract

The interactions between atmospheric vortex pairs are simulated and studied with a nondivergent barotropic model and a three-dimensional tropical cyclone model.

Numerical experiments with nondivergent barotropic vortex pairs show that the relative movements of the vortices are sensitive to the separation distance and the characteristics of the swirling wind of the vortex. No mutual attraction is found in any of the nondivergent barotropic vortex pairs tested.

Results from the three-dimensional tropical cyclone model show that on a constant ƒ-plane with no mean wind, the movements of the two interacting tropical cyclones consist of a mutual cyclonic rotation, attraction and eventual merging, in agreement with Fujiwhara's description. The displacement of one interacting storm in the mutual rotation is proportional to the combined strength of the binary system, but inversely proportional to the size of the storm and to the square of the separation distance. The rate of merging is related to the development of a mean secondary circulation on the radial–vertical plane, and is quite independent of the strength of the two tropical cyclones.

The latitudinal variation of the Coriolis parameter adds a northwest beta drift to the trajectories. Depending on their relative strength and location, the beta drift either speeds up the merging process or separates the two interacting tropical cyclones.

Abstract

The interactions between atmospheric vortex pairs are simulated and studied with a nondivergent barotropic model and a three-dimensional tropical cyclone model.

Numerical experiments with nondivergent barotropic vortex pairs show that the relative movements of the vortices are sensitive to the separation distance and the characteristics of the swirling wind of the vortex. No mutual attraction is found in any of the nondivergent barotropic vortex pairs tested.

Results from the three-dimensional tropical cyclone model show that on a constant ƒ-plane with no mean wind, the movements of the two interacting tropical cyclones consist of a mutual cyclonic rotation, attraction and eventual merging, in agreement with Fujiwhara's description. The displacement of one interacting storm in the mutual rotation is proportional to the combined strength of the binary system, but inversely proportional to the size of the storm and to the square of the separation distance. The rate of merging is related to the development of a mean secondary circulation on the radial–vertical plane, and is quite independent of the strength of the two tropical cyclones.

The latitudinal variation of the Coriolis parameter adds a northwest beta drift to the trajectories. Depending on their relative strength and location, the beta drift either speeds up the merging process or separates the two interacting tropical cyclones.

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