Trends of western North Pacific Tropical Cyclone Outflow Height and Temperature under Global Warming

Relatively little is known about the impact of global warming on the tropical cyclone (TC) outflow, despite its large contribution to TC intensity. In this study, based on the IBTrACS dataset and ERA5 reanalysis data, we show that TC outflow height has risen significantly in the past decades (1959-2021) over the western North Pacific, and the rising trend tends to be sharper for stronger TCs. This rising trend of the outflow height explains the contradiction between the decrease trend of the TC outflow temperature and the increase trend of the atmospheric troposphere temperature. Moreover, the possible contribution of TC outflow height trend to TC intensity has also been investigated. The results show that the rise of outflow height leads to the decrease of outflow temperature, and thus an increased difference between underlying sea surface temperature (SST) and TC outflow temperature, which eventually favors the increase of TC intensity.