EAPS

Understanding the response of tropical cyclones to climate: seeds and genesis. 

A suite of global climate model experiments with different climate models, and across different atmospheric resolutions, model physics and levels of coupling, are performed in order to better understand the response of tropical cyclones (TCs) to global-scale forcing, including the coupled response to CO2 doubling. In addition to experiments with complex surface forcing structure, simplified perturbation experiments with uniform warming, isolated CO2 increase (with SST fixed), are performed with the models to further understand the sources of inter-model spread.

Isolated doubling of CO2 drive decreases in global TC frequency across models and configurations, but the response to warming and patterns of temperature change depends strongly on model configuration - even though large-scale changes in TC-relevant factors (such as shear, entropy deficit and potential intensity) are similar. These complex responses of global TC frequency arises due largely competing influences of the number of precursive disturbances ("TC seeds") and the probability of genesis given a seed as determined by the large-scale environment - accounting for only one or the other fails to explain the range modeled TC changes. Theories to understand global and regional TC frequency should account for the factors controlling TC seeds, in addition to the probability of genesis.