The weakening seasonality of Indo-Pacific warm pool size in a warming world since 1950

Abstract The seasonal variation of Indo-Pacific warm pool (IPWP) plays an important role in the oceanographic and climatological processes. While the IPWP expansion under greenhouse warming has been widely discussed, the response of the IPWP seasonality to climate change has received limited attention. In this study, we found an obvious seasonal diversity in the IPWP expansion from 1950–2020, with a maximal (minimal) expansion trend of 0.28×107 km2/decade in winter (0.17×107 km2/decade in spring), which consequently reduces the seasonality amplitude of the IPWP size variation. This is primarily attributed to the seasonal difference in the climatological spatial SST pattern over the Indo-Pacific Ocean, especially that over the tropical Indian Ocean, which determines the capacity for the IPWP expansion. Heat budget analyses show that the seasonal shortwave radiation and latent heat fluxes are the major factors controlling the capacity for IPWP size change across seasons. The presented analyses emphasize the significant weakening of the seasonality of the IPWP size, which may have great impacts on IPWP ecological environment and tropical climate system, and remind that the intrinsic properties of the climate background of Indo-Pacific SST hold important clues on the IPWP expansion under climate change.