资源环境科技发展态势分析平台

Tropical cyclones (TCs) form within a closed circulation region of large-scale disturbances under certain dynamical and thermodynamical conditions. This study investigates differences in the large-scale environmental conditions of a TC 48 hr before the declaration of tropical depression, comparing those that developed into tropical storms (TSs) with those depressions that did not develop. Here, we apply the Okubo-Weiss Zeta Parameter detection and tracking scheme to ERA-interim reanalysis from 1989-2018, across different ocean basins. The method detects storm-system-scale environmental conditions that favor TC formation. We construct spatial composites of thermodynamical and dynamical quantities for both developing and nondeveloping depressions, as well as storm-relative streamlines. A statistical index (the Box Difference Index) is used to quantitatively estimate the dominant limiting factors of TS formation from the area-averaged quantities of large-scale variables. The relative contribution of large-scale environmental variables impeding the development of an initial tropical depression to TS differs between ocean basins perhaps due to regional variations in the characteristics of large-scale disturbances and the surrounding environmental conditions. A streamline analysis shows that the developing storms have a more pronounced cyclonic core and are protected from external influences by a stronger shear sheath layer surrounding the core extending from the lower to middle troposphere. This study, therefore, identifies the potential limiting variables and structural differences in an initial circulation that impede TS formation across different ocean basins.

Plain Language Summary Tropical cyclones form under certain atmospheric conditions within different large-scale disturbances across various ocean basins. Every year a large number of tropical disturbances form across global ocean basins, but only a few of them develop into tropical cyclones, with a geographical variation in the number of formations. Previous studies on the differences in the environmental conditions of developing versus nondeveloping tropical disturbances focus on the Atlantic and Pacific Ocean basins due to less observations in other ocean basins. The recent development of the "marsupial pouch" theory of tropical cyclone formation has led to the development of a detection scheme to identify the locations within large-scale disturbances that have the potential for tropical cyclone formation. The detection scheme is tuned to detect the initial tropical depressions in addition to the developed tropical storms. This scheme helps us to investigate the environmental differences between developing and nondeveloping tropical depressions in all the ocean basins. The environmental variables inhibiting tropical storm formation differ among ocean basins, with structural differences from the lower to upper troposphere disrupting sustained convection in nondeveloping cases. This study, therefore, identifies the potential limiting factors for tropical storm formation across different ocean basins.