Title: Tropical cyclogenesis in environments of radiative-convective equilibrium




Abstract: Two methods have been developed to explore tropical cyclogenesis with
climate change. One is to count and track tropical cyclone-like vortices
in global climate models. A second is to use quantities thought to be
relevant to tropical cyclogenesis, combined through statistical analysis,
to provide an index related to the likelihood of genesis for a given
environment, termed the genesis index. Both of these methods use large
scale fields with insufficient resolution to incorporate processes
fundamental to genesis. In order to obtain high resolution details of
variations in the genesis process with climate, we resolve the cloud scale
while approximating the large scale with a state of radiative convective
equilibrium (RCE). RCE provides a useful approximation to the large scale
tropical state since the temperature and moisture profiles are largely
controlled by the sea surface temperature (SST) and the mean surface wind.




The thermodynamic aspects of tropical cyclogenesis are explored through
the relationship between a genesis parameter determined by the RCE state
and a genesis proxy. A genesis proxy is taken to be a measure of the
likelihood of tropical cyclone formation from a pre-existing mid-level
disturbance in RCE environments through the use of high resolution
numerical model simulation. Furthermore, the components of the genesis
parameter will be directly tied to the success or failure of simulated
genesis.




To elucidate the kinematic aspects of genesis, the orientation of the
shear with respect to the mean surface wind is varied in an array of
numerical simulations. It will be shown that the role of shear orientation
is as influential on genesis as the mean surface wind and SST. A detailed
diagnosis of the simulated genesis process will be presented in addition
to the sensitivity of genesis to the magnitude of the vertical shear.