Thermodynamic control of tropical cyclogenesis in environments of radiative‐convective equilibrium with shear

Abstract

AbstractThe potential for tropical cyclone formation from a pre‐existing disturbance is further explored with high‐resolution simulations of cyclogenesis in idealized, tropical environments. These idealized environments are generated from simulations of radiative‐convective equilibrium with fixed sea‐surface temperatures (SSTs), imposed mean surface winds, and an imposed profile of vertical wind shear. The propensity for tropical cyclogenesis in these environments is measured in two ways: first, in the period of time required for a weak, mid‐level circulation to transition to a developing tropical cyclone; and second, from the value of an incubation parameter that incorporates environmental measures of mid‐level saturation deficit and thermodynamic disequilibrium between the atmosphere and ocean. Conditions of tropospheric warming can be produced from increased SSTs or from increased mean surface winds; in either case, the time to genesis increases with atmospheric warming. As these parameters are varied, the incubation parameter is found to be highly correlated with changes in the time to genesis.The high resolution (3 km) of these simulations permits analysis of changes in tropical cyclogenesis under warming conditions at the vortex scale. For increasing SST, increased mid‐level saturation deficits (dryness) are the primary reason for slowing or preventing genesis. For environments with increased surface wind, it is the decreased thermodynamic disequilibrium between the atmosphere and ocean that delays or prevents development. An additional effect in both cases is a decoupling of the low‐level and mid‐level vortices, primarily as a result of increased advecting flow at the altitude of the mid‐level vortex, which is linked to the height of the freezing level. Copyright © 2010 Royal Meteorological Society