Unfavorable environmental conditions for tropical cyclone genesis over the western North Pacific during the Last Interglacial based on PMIP4 simulations

Investigating the variation in tropical cyclone (TC) activity over the western North Pacific (WNP) in past warm periods helps to better understand TC behaviors in a warming future. In this study, the authors analyze the changes in large-scale TC genesis factors and the associated mechanisms over the WNP during the Last Interglacial (LIG), based on multimodel outputs from the Paleoclimate Modelling Intercomparison Project Phase 4. The results show that potential intensity exhibits a general decrease over the WNP during the LIG in the storm season, dominated by a weakened thermodynamic disequilibrium. The moist entropy deficit shows an overall increase over the WNP, arising from the decreased mid-tropospheric moisture and weakened vertical temperature contrast. Vertical wind shear enhances over the central WNP but weakens over the southwestern WNP, which is induced by the changes in the meridional tropospheric temperature gradient and hence high-level zonal winds. The absolute vorticity shows a general decrease over the WNP, partially linked with the decreased SST over the western tropical Pacific. Based on a genesis potential index, the authors suggest a decrease in genesis potential over the WNP during the LIG, indicating unfavorable conditions for TC genesis. The results highlight the important role of Earth's orbit in regulating TC activity, which may shed light on TC behaviors in a warmer climate.