Conceptual Evolution of the Theory and Modeling of the Tropical Cyclone

Dynamically, the tropical cyclone is a mesoscale power plant with a synoptic-scale supportive system. By the early 1960's, the general structure and energetics of the system and basic components of the supportive mechanism were fairly well documented by the instrumented aircraft observation of hurricanes and through the diagnostic interpretation of the data. The prognostic theory which would have unified these basic findings in a dynamically coherent framework had a more difficult time emerging. When a viable theory finally emerged, a change in the theoretical perception of the problem was necessary. The parameterization of cumulus convection was an important technical factor in the reduction of a multiscale interaction problem to a mathematically tractable form. Nevertheless, it was the change in our perception of the basic problem and the re-arrangement of priorities that made the parameterization a tolerable substitute for real clouds. Even then, the validity and limitation of the new theory, known as CISK, were fully appreciated only through careful experiments with nonlinear numerical models. In the meantime, the mathematical simplicity of certain parameterization schemes enticed many to apply the schemes to other tropical disturbances, including the easterly wave, in the traditional idiom of linear stability analysis. More confusion than enlightenment often ensued as mathematics overran ill-defined physics. With further advances in numerical modeling, the interest in tropical cyclone research shifted from conceptual understanding of an idealized system to quantitative simulation of the detail of real cyclones, and it became clear that the intuitive parameterization of whole clouds would have to be discarded. Now that some models have returned to explicit calculation of the cloud scale, one may wonder if all the exercises with parameterized convection were an unfortunate detour in the history of tropical cyclone modeling. The answer depends on one's philosophical view of "progress."