Effects of Tropospheric Temperature Structure on the Intensification of Tropical Cyclones

The characteristics of the environment surrounding tropical cyclones (TCs) vary with time and space at various scales. In a future climate condition under global warming, it is projected that the tropospheric stability will change. It is known that the change in the intensity of TCs greatly depends on environmental conditions. However, the physical mechanisms for the intensity change are not fully understood, and therefore further investigations are required. In our recent study on the future change of Typhoon Vera (1959), a category-5 storm that devastated the Japanese islands, it was shown that the increases in water vapor, sea surface temperature and tropopause-height due to global warming lead to taller and stronger TCs with deeper convection. Therefore, in this study, we investigate the influences of environmental stability, i.e., the tropospheric temperature structure, on the change in the intensity of TCs by using an axisymmetric non-hydrostatic model (Cloud Model Version 1: CM1). Specifically, we focused on effects of tropospheric temperature lapse rate, tropopause-level temperature, and tropopause-height on the evolution and intensity of TCs by conducting a series of numerical experiments in which those tropospheric parameters are systematically changed. It was found that with the decrease in the tropopause-level temperature and the increase in tropopause-height but with a larger lapse rate condition lead to the increase in the TC intensity. In contrast, in the cases of increasing the tropopause-height by keeping the tropopause-level temperature unchanged, the intensity of TCs tends to decrease due to the decrease in temperature lapse rate. The most significant feature is that the maximum intensity and the intensification rate of the simulated TCs clearly increase with the increase in temperature lapse rate. From these sensitivity experiments, it is shown that the temperature lapse rate has the most significant impacts on the change in the TC intensity.