Increased sensitivity of tropical cyclogenesis to shear in higher SST environments. Part I: Simulation design and primary results

A new method for evaluating the sensitivity of tropical cyclone (TC)genesis to environmental parameters was recently presented, which involves the simulation of tropical cyclone development with a cloud-resolving model in environments of radiative-convective equilibrium (RCE) generated by the same model. This method is extended to allow for the incorporation of mean wind shear into the RCE states, thus providing much more realistic and relevant simulations of TC genesis. The "finite-amplitude" nature of tropical cyclogenesis is reproduced, with cyclogenesis resulting only when the initial vortex is above some strength, which in turn depends on the environmental parameters. For fixed thermodynamic parameters, the required initial vortex strength necessary to achieve genesis increases with the mean wind shear. However, an unexpected result has been obtained, that this sensitivity to shear increases as the sea surface temperature increases: increasing ocean temperature does not allow TC genesis to overcome larger shear. In fact, the opposite trend is found, that the initial amplitude required for TC genesis in shear is larger when the SST is higher.

The mechanisms for the increased sensitivity to shear and other applications of our technique will be presented in Part II.