Increased sensitivity of tropical cyclogenesis to shear in higher SST environments. Part II: Mechanisms and other applications

The methodology described in Part I of this study is applied to idealized simulations of tropical cyclogenesis using initial conditions composed of various vertical wind shear profiles and sea-surface temperatures (SSTs) in an environment where the troposphere is in radiative-convective equilibrium (RCE) with the sea surface. The increased sensitivity of tropical cyclogenesis to vertical shear at higher SSTs is found to be a consequence of the sensitivity of the thermal profile to SST. The height of the stratiform precipitation region of the initial mesoscale convective system, vital to the development of a mid-tropospheric vortex, is located just above the freezing level, which raises in altitude as the SST increases. This leads to a decreased coupling with the surface vortex, due to the greater distance and the increased shear at that altitude. Using a multitude of vertical wind shear orientations, a general mapping of the sensitivity of tropical cyclogenesis to wind shear in RCE environments is provided.

The same methodology is applied to a suite of global climate models used for the Intergovernmental Panel on Climate Change 4th Assessment Report. The soundings are derived from the mean model output from August to October over two time periods, 2001-2020 and 2081-2100. Results are presented for the Gulf of Mexico, Western Caribbean, and other locations.