In recent years, atmospheric modeling has begun to move from pure finite difference and spectral methods to semispectral methods utilizing finite differences in one coordinate and spectral methods in another. While the effectiveness of the pure methods for atmospheric problems is fairly well documented, comparatively little work has been done on the effectiveness of semispectral schemes. This is particularly evident in atmospheric vortex problems dealing with the dynamics of the hurricane near-core region. Because of the nearly circular flow of a strong hurricane, we hypothesize that a semispectral formulation for hurricane-like vortices (i.e., finite difference in the radial direction and spectral in the azimuthal direction) may prove useful in understanding the asymmetric dynamics of the near-core region. In this talk, we examine the semispectral approach for its effectiveness in simulating polygonal eyewall and vorticity mixing dynamics.
We investigate the semispectral method's effectiveness using an f-plane, nondivergent, barotropic, vorticity equation model which is an extension of Montgomery and Kallenbach (1997). We perform various runs of the model and compare our results to the pure finite difference results of Montgomery and Enagonio (1998) and the pure spectral results of Schubert, et al (1998). Based on these experiments, we assess the strengths and weaknesses of the semispectral approach in simulating hurricane near-core dynamics.
REFERENCES:
Montgomery, M. T., and J. Enagonio, 1998: Tropical cyclogenesis via
convectively forced vortex Rossby waves in a three-dimensional
quasigeostrophic model. J. Atmos. Sci., in press.
Montgomery, M. T., and R. J. Kallenbach, 1997: A theory for vortex
Rossby waves and its application to spiral bands and intensity
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Schubert, W. H., Montgomery, M. T., Taft, R. K., Guinn, T. A., Fulton,
S. R., Kossin, J. P., and J. P. Edwards, 1998: Polygonal
eyewalls, asymmetric eye contractions and potential vorticity
mixing in hurricanes. J. Atmos. Sci., in press