The Indo-Pacific warm pool (IPWP) is enclosed by a 28 °C isotherm and plays a vital role in controlling atmospheric circulations. However, the effects of changes in regional warm pool sea surface temperatures (SSTs) remain unexplored. We divided the IPWP into the Indian and Pacific sectors and distinguished their responses to natural variability and global warming. Furthermore, we examined the impacts of the interannual variability (IAV) in warm pool SST on the tropical Hadley, Walker, and monsoon circulations. The Hadley circulation was affected by warm pool SST warming, i.e., warmer SSTs over the warm pool strengthened the upward branch of Hadley circulation, whereas the downward branch was respectively weakened and strengthened in the Northern and Southern Hemispheres. Walker circulation was strengthened (weakened) in the warming (natural) mode. Consequently, the Walker circulation is weakened since the natural variability of warm pool SST plays a more dominant role rather than the warming trend of SSTs over the warm pool. Furthermore, our analysis displays that warm pool warming has little impact on the monsoon circulation. Our findings highlight the different roles of the IAV of warm pool regions in each tropical circulation as part of the warming trend and natural variability.

The Indo-Pacific warm pool (IPWP) is a region known for its strong atmospheric convection, which plays a key role in global climate. However, in recent decades, the IPWP has experienced human-induced warming, and it has been observed to have a non-linear relationship between sea surface temperature (SST) and precipitation. Despite the rising SSTs, the increase in precipitation is limited until a specific SST, which is defined as saturation threshold SST (STT). The STT indicates a distinct transition before and after the STT, highlighting the non-linear response of precipitation to SST. Nevertheless, the impact of warmer climates on the SST-precipitation relationship and STT remains uncertain. To investigate future changes in this relationship, we analyzed a joint distribution of SST and precipitation using the historical data and three different Shared Socioeconomic Pathway (SSP) scenarios (SSP2-4.5, SSP3-7.0, and SSP5-8.5). We examined the near future (2041–2060), and far future (2081–2100). Our findings reveal that the STT increases with the shift in mean state due to the involvement of atmospheric stratification. This increase is observed across all three scenarios in both future periods, with the SSP5-8.5 scenario exhibiting the most substantial rise during the far future. The warming climate leads to a more pronounced warming in the upper troposphere than the surface, resulting in tropospheric stabilization. This process contributes to the increase in STT through moist-adiabatic lapse rate adjustment. Additionally, the weakening of vertical motion constrains the increase in precipitation, despite the availability of abundant moisture. This study sheds light on the changing SST-precipitation relationship and provides a possible mechanism for the limited increase in precipitation. Therefore, this study offers a background for a better understanding of the non-monotonic response of precipitation to SST in the context of climate change.

Tropical sea surface temperature warming displays distinct regional patterns, but its influence on Madden-Julian Oscillation propagation remains unclear. Here we investigate how a shift toward La Niña-like conditions around 1999 has affected Madden-Julian Oscillation propagation by comparing two periods: 1979–1998 and 2003–2022. Using satellite observations and reanalysis data, we show that propagation accelerated over the Indian Ocean and the Maritime Continent but slowed over the western Pacific in the later period. These contrasting responses are linked to changes in sea surface temperature patterns and associated atmospheric conditions. Over the Indian Ocean, enhanced low-level horizontal moisture gradients and increased upper-tropospheric stability facilitate propagation, while weakened moisture gradient and suppressed convection hinder it over the western Pacific. Despite complex terrain and atmospheric interactions over the Maritime Continent, background changes still favor enhanced propagation. These findings highlight the sensitivity of Madden-Julian Oscillation behavior to regional ocean–atmospheric conditions, with implications for improving subseasonal prediction.

The Madden-Julian Oscillation (MJO) is a crucial atmospheric phenomenon characterized by large-scale, eastward-propagating disturbances in the tropical atmosphere. It profoundly influences global climate and weather patterns and serves as a key source of predictability for subseasonal forecasts. In particular, the propagation characteristics of the MJO are critical parameters that impacts the timing and intensity of its effects. Variability in these characteristics can alter the MJO’s interaction with other climate components, thereby affecting weather patterns. Therefore, it is essential to investigate the variability of MJO propagation characteristics. In this study, we aim to examine the changes in propagation characteristics of the MJO, such as propagation speed, across three primary regions: Indian Ocean, Maritime Continent, western Pacific. These changes will be compared between two distinct period (P1: 1979-1998, P2: 2003-2022). Furthermore, we will investigate the mechanisms driving variations in MJO propagation speed within each tropical region and assess potential future changes using reanalysis data and model outputs. By addressing these questions, this study can contribute to improve the predictability and accuracy of climate models in representing the MJO.

The Indo-Pacific warm pool (IPWP) is enclosed by a 28 ◦C isotherm and plays a vital role in controlling tropical circulations. However, the effects of changes in regional warm pool sea surface temperatures (SSTs) on the circulations remain unexplored. To do this, we divided the IPWP into the Indian and Pacific sectors and distinguished their responses to natural variability and global warming. And then, we examined the impacts of the interannual variability (IAV) in warm pool SST on the tropical Hadley, Walker, and monsoon circulations. The Hadley circulation was affected by warm pool SST warming, i.e., warmer SSTs over the warm pool strengthened the upward branch of Hadley circulation, whereas the downward branch was weakened and strengthened in the Northern and Southern Hemispheres. Walker circulation was strengthened (weakened) in the warming (natural) mode. Consequently, the Walker circulation is weakened since the natural variability of warm pool SST plays a more dominant role than the warming trend of SSTs over the warm pool. It is notable that warm pool warming has little impact on monsoon circulation. Our findings highlight the different roles of the IAV of warm pool regions in each tropical circulation as part of the warming trend and natural variability. Furthermore, an increase in precipitation is limited up to a specific SST, although SST becomes warmer. We defined this specific SST as Saturation Threshold SST (STT). Under a warming climate, future changes in STT over the IPWP and its mechanism will be shortly shown in this presentation.