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.

Seasonal Diversity of Indo-Pacific Warm Pool Volume Expansion: The Role of Climatological Subsurface Temperature Patterns

“…In the following, we try to dig into the problem by conducting a set of sensitivity experiments which assume different ideal conditions of topical Indo-Paci c Oceanic warming. Previous researches have de ned the capacity for warm pool expansion 22,54 and revealed its signi cant in uence on the seasonal difference in surface IPWP expansion 24 . In this section, we nd that the seasonal diversity in the capacity for IPWP volume expansion, which is determined by the spatial characteristics of climatological subsurface ocean temperature, is the primary driver of the seasonally different IPWP expansion trends.…”

“…This observation unveils a crucial information: the cooler subsurface temperature background in autumn and winter during P1 allows for a larger spatial extent for IPWP expansion in these two seasons during P2. In line with the de nition from previous researches on such spatial extent for warm pool expansion, we adopt the concept of the capacity for warm pool volume expansion 22,24,54 (see Methods). That is to say that the capacity for IPWP volume expansion may be greater in autumn and winter compared to spring and summer, as these seasons have more grids with temperatures around 28°C (Fig.…”

“…The capacity for volume change is regarded as the potential for the 3D warm pool body expansion 22,24,54 and is determined by the climatological ocean temperature pattern over tropical Indo-Paci c Ocean. Here, by assuming that the warming of tropical Indo-Paci c is spatially and seasonally uniform (the assumptions of the SSUE), we can quantitatively calculate the capacity for change of IPWP, IOWP and WPWP whose seasonality is merely determined by the climatological ocean temperature pattern over tropical Indo-Paci c, Indian, western Paci c Ocean.…”

“…In particular, it was recently discovered that the surface IPWP size expansion exhibits signi cant seasonal diversity, which leads to a decrease in the seasonality of surface IPWP size and further impacts on the Walker circulation 24 . The changing seasonality of IPWP size is of particular importance due to its crucial role in modulating the seasonal cycle of atmospheric circulation 6, 24,28,42 .…”

Observed northward shift of large hailstorms in the eastern United States since 2000

“…Given the nonzero trend in the hail event counts over the whole eastern US, the ordinary probability density function (PDF, or image histogram) and spatial PDF (SPDF) method [51][52][53] could visualize the changes in the spatial distribution of hail activity, neglecting the overall hail occurrence trend. In the calculation of the PDF of hail event latitude, the probability (𝑃𝐷𝐹 𝑦𝑒𝑎𝑟 ) that a hail event is observed at a certain latitude (𝑙𝑎𝑡 0 ) in a year is estimated by the number of hail event counts at…”