Uptrend of the Western North Pacific Tropical Cyclone Outflow Height during 1959–2021

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 International Best Track Archive for Climate Stewardship (IBTrACS) dataset and ERA5 reanalysis data, we show that the TC outflow height has risen significantly (48.20 ± 22.18 m decades⁻¹) in the past decades (1959–2021) over the western North Pacific, and the rising trend tends to be sharper for stronger TCs (the uptrend of severe typhoon is 61.09 ± 40.92 m decades⁻¹). 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, possible contribution of the TC outflow height uptrend 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.