THE RESPONSE OF A TROPICAL CYCLONE MODEL TO VARIATIONS IN BOUNDARY LAYER PARAMETERS, INITIAL CONDITIONS, LATERAL BOUNDARY CONDITIONS, AND DOMAIN SIZE

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.