The effects of relative versus absolute SST on tropical cyclone potential intensity using a single column model

We investigate the comparative effects of relative and absolute sea surface temperature (SST) on tropical cyclone potential intensity, using the Bony-Emanuel single column model. The model is run in two modes: (i) a radiative convective equilibrium (RCE) mode to represent the convective response to uniform warming of the ocean, as in an homogeneous aqua planet, and (ii) a weak temperature gradient (WTG) mode to represent the convective response to warming over a limited area of ocean relative to the tropical mean SST. The potential intensity is then computed using model output (temperature and moisture profiles) for various values of SST, ranging from 25°C to 30°C. The results show that potential intensity change is more sensitive to changes in relative SST than to changes in absolute SST, with slopes of between about 6 and 8 m s-1 °C-1 in the WTG simulations and about 1 m s-1 °C-1 in RCE. The increased sensitivity of potential intensity to SST in the WTG simulations can be attributed primarily to an increase in the air-sea disequilibrium, which arises from stronger convective downdrafts and higher instability, relative to the RCE simulations.