Understanding the Variation and Mechanisms of Tropical Cyclone Genesis Potential over the Western North Pacific during the Past 20 000 Years

Abstract

To deepen our understanding of the behavior of tropical cyclones (TCs) over the western North Pacific (WNP) and its response to various external forcings, we investigate the variation of TC genesis potential over the WNP during the past 20 ka that experienced several large forcings. Using a set of transient simulations and a genesis potential index, our results indicate that TC genesis potential in the storm season shows an overall increase averaged over the WNP during the Heinrich Stadial 1 (HS1; ~17−16 ka) relative to the last glacial maximum. Subsequently, there is a sharp decrease in genesis potential during the Bølling-Allerød (BA; ~13.5 ka) relative to the HS1, which is followed by an increase during the Younger Dryas (YD; ~12.9−11.7 ka). During the Holocene, TC genesis potential shows a slight decrease during the early–middle Holocene (~11.7−6 ka), while a significant increasing trend afterwards. Further analysis shows that the contribution of each genesis factor to the genesis potential change varies greatly with time, which is in turn tied to changes in external forcings. The increased meltwater fluxes dominate the increased genesis potential during the HS1 and YD, whereas all external forcings (i.e., changes in meltwater, ice sheets, CO2, and insolation) contribute to genesis potential change during the BA. The long-term increasing trend from the mid-Holocene to the present is controlled by orbital insolation. These results may help improve our understanding on past TC activity and shed lights on TC response to various external forcings in a long-term future.