Despite decades of theoretical research and observational studies, a good understanding of tropical cyclone genesis(TCG) remains elusive. One school of theories proposes that TCG within an African Easterly Wave result...Despite decades of theoretical research and observational studies, a good understanding of tropical cyclone genesis(TCG) remains elusive. One school of theories proposes that TCG within an African Easterly Wave results from “bottom-up” development of cyclonic vorticity that is contingent upon favorable conditions in the lower-troposphere and boundary layer. Our observational study suggests that while lower-tropospheric forcing is a necessary condition for this type of TCG, it may not be sufficient in some cases, and that environmental conditions in the upper levels can have an influence. Specifically, we find evidence to suggest that pre-TCG upper-tropospheric flow patterns characterized by core-connecting outflow vents to the environment can in certain situations provide a modulating effect on Atlantic tropical disturbances trying to develop. Patterns of nearenvironment upper-level inertial stability, divergence, outflow setup, and mass evacuation are identified and related to surface development. The study employs high-resolution satellite-derived wind data, aircraft GPS dropwindsondes, composite fields, multivariate objective analyses, and case studies to help identify conditions in the upper-level environment that can play a role in Atlantic TCG events.展开更多
文摘Despite decades of theoretical research and observational studies, a good understanding of tropical cyclone genesis(TCG) remains elusive. One school of theories proposes that TCG within an African Easterly Wave results from “bottom-up” development of cyclonic vorticity that is contingent upon favorable conditions in the lower-troposphere and boundary layer. Our observational study suggests that while lower-tropospheric forcing is a necessary condition for this type of TCG, it may not be sufficient in some cases, and that environmental conditions in the upper levels can have an influence. Specifically, we find evidence to suggest that pre-TCG upper-tropospheric flow patterns characterized by core-connecting outflow vents to the environment can in certain situations provide a modulating effect on Atlantic tropical disturbances trying to develop. Patterns of nearenvironment upper-level inertial stability, divergence, outflow setup, and mass evacuation are identified and related to surface development. The study employs high-resolution satellite-derived wind data, aircraft GPS dropwindsondes, composite fields, multivariate objective analyses, and case studies to help identify conditions in the upper-level environment that can play a role in Atlantic TCG events.
