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

Seasonal variation of the Indo-Pacific warm pool (IPWP) plays an important role in oceanographic and climatological processes. While expansion of the IPWP under greenhouse warming has been widely discussed, the response of IPWP seasonality to climate change has received limited attention. In this study, we found an obvious seasonal diversity in expansion of the IPWP from 1950 to 2020, with a maximum (minimum) expansion trend of 0.28 x 7 km(2)/decade in winter (0.17 x 7 km(2)/decade in spring), which consequently reduces the seasonality amplitude of the variation in IPWP size. This is primarily attributed to the seasonal difference in the climatological spatial sea surface temperature (SST) pattern over the Indo-Pacific Ocean, especially that over the tropical Indian Ocean, which determines the capacity for IPWP expansion. Heat budget analyses show that the seasonal shortwave radiation and latent heat fluxes are the major factors controlling the capacity for change in IPWP size across seasons. The presented analyses emphasize the significant weakening of the seasonality of IPWP size, which may have great impacts on the ecological environment of the IPWP and the tropical climate system, and remind us that the intrinsic properties of the climate background of Indo-Pacific SST hold important clues about IPWP expansion under climate change.