An Observational Study of Environmental Dynamical Control of Tropical Cyclone Intensity in the Atlantic

Abstract

An attempt has been made to extend the analysis of environmental dynamical control of tropical cyclone (TC) intensity recently performed for the western North Pacific to the North Atlantic. The results show that both the vertical shear and translational speed have negative effects on TC intensity, which is consistent with previous findings for other basins. It shows that few TCs intensified when they moved faster than 15 m s?1. The threshold vertical shear of 20 m s?1?defined as the difference of total winds between 200 and 850 hPa averaged within 5° latitude around the TC center?is found above which few TCs intensified and below which most TCs could reach their lifetime peak intensity. The average intensity of total TCs in the Atlantic is a bit smaller than that in the western North Pacific. The SST-determined empirical maximum potential intensity (EMPI) for a TC for 1981?2003 in this study is slightly higher than that found for 1962?92 by DeMaria and Kaplan in the Atlantic, however. To be consistent with the theoretical TC MPI, a new EMPI has been constructed, which includes the effect of thermodynamic efficiency. This new EMPI marginally improves the estimation of real TC maximum intensity because the thermodynamic efficiency is largely determined by SST. To include the environmental dynamical control of TC intensity, a dynamical efficiency has been introduced, which is inversely proportional to the combined amplitude of the vertical shear and translational speed. With this dynamical efficiency, an empirical maximum intensity (EMI) for Atlantic TCs has been constructed. This EMI includes not only the positive contribution by SST but also the effects of both thermodynamic and dynamical efficiencies, and it provides more accurate estimations of TC maximum intensity. Furthermore, the formulation of the new EMI explains the observed behavior of TC maximum intensity by thermodynamic and dynamical controls in a transparent and easy-to-interpret manner.