Dependence of tropical cyclone intensification rate on sea-surface temperature

The dependence of tropical cyclone intensification rate on the sea-surface temperature (SST) is examined in the prototype problem for tropical cyclone intensification on an f-plane using a three-dimensional, non-hydrostatic numerical model. The effects of changing the SST are compared with those of changing the latitude examined in a recent article. It is found that the dependence of intensification rate on latitude is largest when the SST is marginal for tropical cyclone intensification (26 degrees C) and reduces in significance as the SST is increased. Further, at a given latitude, intensification begins earlier and the rate of intensification increases with increasing SST, on account of a significant increase of surface moisture fluxes from the warmer ocean. These higher fluxes result in higher values of near-surface moisture and equivalent potential temperature, leading to a larger radial gradient of diabatic heating rate in the low to middle troposphere above the boundary layer. This larger radial gradient leads to a stronger overturning circulation, which in turn leads to a stronger radial import of absolute angular momentum surfaces and therefore more rapid spin-up. These arguments invoke the classical axisymmetric spin-up mechanism. Non-axisymmetric issues are touched upon briefly.