An investigation of rotational influences on tropical‐cyclone size and intensity

Abstract

AbstractWe investigate the rotational constraint on the intensity and size of a tropical cyclones using a minimal, three‐layer, axisymmetric tropical‐cyclone model. In the first of two sets of experiments, the same initial baroclinic vortex is spun up in a quiescent environment with different levels of background rotation, characterized by the Coriolis parameter, f. It is found that the strongest vortices, as characterized by their final intensity, develop in environments with intermediate background rotation. It is found also that there exists a similar optimum background rotation strength to obtain the largest storm as measured by the radius of gale‐force winds. These results appear to be in line with those of classical laboratory experiments by Turner and Lilly, an analogy that we explore in the present article. While the analogy is found to have certain limitations, including the fact that spin‐up of the maximum tangential winds in the inner‐core in the model takes place in the boundary layer, the study raises aspects of tropical‐cyclone dynamics that we believe to be of fundamental importance and require further investigation.As an aid to understanding the foregoing results, a second set of calculations is carried out with the vortex forced by a prescribed radial profile of diabatic heating rate typical of that in the first set and with other moist processes excluded. For this distribution of heating rate, there is no optimum background rotation rate for intensity within a realistic range of values for f, implying that the relationship between the forcing strength and rotation strength is an important additional constraint in tropical cyclones. However, in these experiments, there is an optimum latitude for size, comparable with that in the first set of experiments. An interpretation is offered for these findings. Copyright © 2011 Royal Meteorological Society