Impact of the tropopause temperature on the intensity of tropical cyclones

This study investigates the impact of the tropopause temperature on the intensity of idealized tropical cyclones (TCs) superimposed on background states of radiative-convective equilibrium (RCE) in a 3D mesoscale model. Simulations are performed with constant sea surface temperature, and an isothermal stratosphere with constant tropopause temperature. The potential intensity (PI) computed from the thermodynamic profiles of the RCE state (before the TCs are superimposed on it) increases 0.4 to 1 m/s for each degree of tropopause temperature reduction. The 3D TC experiments yields intense tropical cyclones whose intensities exceed the PI value substantially. It is further shown that the discrepancy may be largely explained by the super-gradient wind in the 3D simulation. The intensity of these 3D TCs shows a ~ 0.4 m/s increase with one degree cooling in the tropopause temperature in RCE, on the lower end of the PI dependence on the tropopause temperature. Sensitivity experiments with larger horizontal grid spacing 8 km produce less intense TCs, as expected, but similar dependence (~ -0.5 m/s/K) on tropopause temperature. Equilibrium TC solutions are further obtained in 200-day experiments with different values of constant stratospheric temperature. Similar relationships between TC intensity and tropopause temperature are also found in these equilibrium TC solutions. It is also shown that a colder tropopause not only yields more intense TCs, but also leads to larger temporal variability in the TC intensity.