Tropical Cyclone Intensity Potential Increase modulated by Cooling in the Lower Stratosphere

This study elucidates the modulating effect of lower stratospheric cooling on tropical cyclone potential intensity (TCPI) through the lens of high-resolution CMIP6 models. While the influence of sea surface temperature (SST) on tropical cyclone intensity is well-documented, the role of upper atmospheric conditions, particularly in the lower stratosphere, remains incompletely understood. Our research provides a quantitative analysis of the mechanisms driving historical TCPI changes across major cyclone basins, particularly emphasizing the impact of lower stratospheric cooling. We utilize three high-resolution CMIP6 models (HadGEM3-GC31, FGOALS-f3-H, GFDL-CM4C192) with a spatial resolution of 25 km, complemented by five lower-resolution CMIP6 models. Our sensitivity analysis reveals a robust inverse relationship between TCPI and outflow temperature across various ocean basins. Quantitatively, a 1°C decrease in outflow temperature corresponds to TCPI increases ranging from 0.82 m/s in the North Indian Ocean to 0.94 m/s in the Southern Hemisphere. Notably, we observe that recent cooling in the lower stratosphere has significantly contributed to increased TCPI. Our result shows distinct regional variations in the contribution of thermodynamic disequilibrium and tropical cyclone efficiency to TCPI changes. The Northeast Pacific is particularly interesting, which exhibits a unique negative efficiency contribution, contrasting with other basins. Furthermore, high-resolution models demonstrate superior capability in resolving TCPI increases and capturing recent intensification trends. Lower stratospheric cooling modulates TCPI significantly spatially, with the Southern Hemisphere, North Atlantic, and West North Pacific showing the most pronounced TCPI changes. These findings underscore the critical importance of accurately representing lower stratospheric cooling in tropical cyclone intensity predictions and highlight the necessity of high-resolution modeling for robust future climate projections of tropical cyclone activity. In conclusion, this research advances our understanding of the complex interplay between atmospheric dynamics and tropical cyclone intensity and provides valuable insights for improving the accuracy of tropical cyclone forecasting and risk assessment in a changing climate.