Stratospheric influence on tropical cyclone evolution

Physical processes at play in the genesis and evolution of tropical cyclones are conducive to the formation of warm cores at their centres. When the warm anomaly is particularly large in the upper troposphere, it is referred to as a high-level warm core. Previous works documented the generation of high-level warm cores as a consequence of stratospheric air intrusion into the troposphere induced by the upper-level dynamics of a tropical cyclone. However, little attention has been given to their effects on the storm's subsequent evolution. It has been suggested that the presence of a high-level warm core can have opposite effects on tropical cyclone intensity: both strengthening and weakening have been described as possible consequences of its formation. In this study, we examine the role of high-level warm cores in the intensification and dissipation processes of tropical cyclones, as reproduced in numerical models of different complexities, namely the model “System for Atmospheric Modeling” (SAM) run under idealized conditions and the model Nonhydrostatic ICosahedral Atmospheric Model run under realistic conditions following the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains summer protocol. Our results confirm the hypothesis of a stratospheric origin behind the formation of high-level warm cores. Their initial role is shown to be an enhancement of storm intensity, by a lowering of the hydrostatic sea-level pressure (HSLP) associated with the presence of warm air aloft. However, as the warm anomaly intensifies and extends to lower levels, it also increases static stability in the air column, with the consequence of inhibiting convection and ultimately contributing to cyclone dissipation. These findings suggest that high-level warm cores play a dual role in the tropical cyclone life cycle, providing a stabilizing mechanism that can limit cyclone strength and longevity.