On the Role of the Tropopause Height in the Development of a Double Warm Core Structure in Intense Tropical Cyclones

Recent experimental real-time typhoon forecasts in the north Western Pacific (WP) basin using the Hurricane Research and Forecasting (HWRF) model have consistently captured a double warm core (DWC) structure in almost all Super Typhoon cases during the 2012-2014 seasons. This study examines the impacts of the tropopause on the development of such a DWC structure in which an upper warm-core near the tropopause is formed on top of a pre-existing midlevel warm core when TCs become sufficiently strong. By initializing the HWRF model with different monthly averaged sounding profiles in the WP and North Atlantic (AL) basins, it will be shown that the tropopause plays a noticeable role in the development of the DWC structure and subsequent intensity development. Specifically, the lower the tropopause height, the higher the vortex strength and the more distinct the DWC structure would be. The sensitivity of the DWC formation to different tropopause heights is more realized for the mean soundings in the WP basin as compared to those in the AL basin. In particular, late episodes of intensification of the model vortex seem to be strongly related to an upper-inflow layer in the lower stratosphere, which allows the model vortex to efficiently build an upper warm core and further intensify even after the model vortex approaches its maximum intensity limit. In any case, the findings suggest that height of the tropopause should be considered in future study of the TC-climate connection.