Uneven Tropical Ocean Warming Reshapes the Madden–Julian Oscillation and Global Weather Dynamics
The tropical regions of our planet are not just sweltering hotspots; they are pivotal engines driving global weather and climate variability. At the heart of this dynamic system lies the Madden–Julian Oscillation (MJO), an intraseasonal oscillation characterized by expansive clusters of convection, clouds, and intense rainfall bands that propagate eastward across the equatorial oceans. This phenomenon exerts profound influence on a variety of weather systems, modulating tropical cyclones, monsoonal flows, and often extending its reach well beyond tropical latitudes to affect weather across continents and oceans. Precisely understanding the variability and mechanisms controlling the speed and intensity of the MJO is indispensable for enhancing sub-seasonal to seasonal weather and climate predictions.
Recent decades have witnessed a notable divergence in sea surface temperature (SST) trends within tropical oceans. While many regions, including the Indian Ocean and parts of the Maritime Continent, experienced significant warming, large swathes of the central and eastern equatorial Pacific have exhibited comparatively cooler temperatures. This anomalous oceanic cooling bears a resemblance to persistent La Niña conditions, thereby establishing a La Niña–like background state distinctively different from previous decades. Such an asymmetric SST distribution raises compelling questions about its implications for atmospheric dynamics, specifically how these spatial disparities in ocean warming influence the propagation characteristics of the MJO.
Addressing this challenge, researchers from Pusan National University conducted a comprehensive analysis of MJO behaviors over two distinct periods: 1979–1998, representing pre-1999 oceanic conditions, and 2003–2022, encapsulating the era marked by La Niña–like asymmetric warming patterns. Utilizing an integrated approach combining satellite-derived observations, such as outgoing longwave radiation (OLR) as a proxy for convection, along with sophisticated atmospheric reanalysis datasets, the team was able to track and characterize intraseasonal convective variability while correlating these dynamics with changes in sea surface temperatures and atmospheric circulation patterns. Their findings elucidate how uneven ocean warming reshapes the fundamental propagation and intensity features of the MJO.
Professor Kyung-Ja Ha, who led the study, articulated a transformative insight: “The recent asymmetric tropical ocean warming has driven contrasting changes in the regional propagation of the Madden–Julian Oscillation, with faster eastward progression over the Indian Ocean and Maritime Continent, contrasted by a pronounced slowdown over the western Pacific Ocean.” This statement encapsulates the emergence of a complex, regionally heterogeneous response of the MJO to evolving thermal and atmospheric conditions across the tropical belt, an evolution that carries significant ramifications for climate models and forecasting systems.
Mechanistically, the research highlights the critical interplay between atmospheric moisture gradients and stability in modulating MJO dynamics. Over the Indian Ocean, the intensification of horizontal moisture gradients ahead of the propagating convective envelope fosters enhanced pre-moistening—a key process facilitating deeper convection and faster eastward movement. Concomitantly, an increase in upper-tropospheric atmospheric stability acts to sharpen the vertical structure of the MJO, further assisting rapid propagation. The Maritime Continent presents additional complexity due to its intricate mosaic of landmasses and seas; however, even here, the MJO’s eastward movement accelerated, albeit to a lesser extent compared to the Indian Ocean.
Conversely, the western Pacific Ocean showcases a starkly different picture. This region experienced a deceleration of the MJO’s eastward propagation, attributed primarily to weakened moisture gradients and a suppression of vertical motion critical for convective development. Furthermore, a destabilization of the upper atmosphere in this zone reduces the efficacy of moist convective processes, thereby limiting the MJO’s ability to sustain its movement at prior speeds. The combined effect of these atmospheric and oceanic changes essentially reshapes the MJO’s lifecycle regionally, underscoring the sensitivity of tropical convection to shifting ocean surface temperatures.
A pivotal contribution of this study lies in emphasizing atmospheric stability as a vital diagnostic parameter for the MJO’s evolution. Traditionally, moisture supply and large-scale circulation dominated understanding of MJO dynamics; however, this research demonstrates that vertical thermodynamic structure—specifically atmospheric stability—modulates how intraseasonal convection evolves and propagates. By quantifying changes in stability alongside moisture variations, the study provides a more comprehensive framework to represent and predict MJO behavior in coupled ocean-atmosphere models.
The implications for climate science and meteorological applications are profound. Accurate simulation of the MJO’s propagation speed and amplitude is essential for improving forecasts of extreme rainfall events, tropical cyclones, and monsoonal variability. Prof. Ha emphasizes, “Improving how climate models incorporate the effects of asymmetric ocean warming on MJO behavior will enhance the reliability of seasonal-to-decadal predictions concerning rainfall distribution and drought potential.” Achieving this progress would empower governments, planners, and communities to devise more resilient strategies in agriculture, water resource management, and infrastructure development, particularly in regions vulnerable to the severe impacts of erratic tropical weather.
Beyond immediate forecasting benefits, these findings enrich the broader understanding of climate variability in a warming world. By revealing how ocean warming patterns modulate weather-driving oscillations like the MJO, this study contributes to deciphering feedback mechanisms within the Earth system. Such insights are integral to projecting future climate scenarios under continued anthropogenic forcing, where shifts in tropical convection and circulation could trigger unanticipated atmospheric responses globally.
Methodologically, the research harnessed state-of-the-art satellite measurements and atmospheric reanalysis frameworks, capturing nuanced variations in intraseasonal convective activity via outgoing longwave radiation (OLR) anomalies. Simultaneously analyzing sea surface temperature distributions allowed the team to disentangle ocean-atmospheric coupling processes that dictate MJO evolution. Vertical profiles of temperature and humidity further informed assessments of atmospheric stability, enabling a multi-dimensional portrayal of the physical environment conducive or restrictive to MJO progression.
In conclusion, the revelation that uneven tropical ocean warming substantially alters the Madden–Julian Oscillation’s regional propagation heralds a paradigm shift in tropical meteorology. This oscillation, long recognized as a cornerstone of tropical and global weather, now emerges as a sensitive barometer of oceanic thermal asymmetries and their cascading atmospheric consequences. As climate change continues to rewrite Earth’s thermal landscape, understanding and integrating these dynamic feedbacks into predictive models will prove critical for safeguarding communities worldwide from the intensifying vagaries of weather and climate.
This important study was carried out under the auspices of the PNU Global—Learning & Academic Research Institution for Master’s, PhD students, and Postdocs (G-LAMP) Program, embodying cutting-edge interdisciplinary climate science innovation emerging from Pusan National University.
Subject of Research: Not applicable
Article Title: Recent asymmetric tropical ocean warming has altered regional propagation of Madden-Julian Oscillation
News Publication Date: 14-Aug-2025
Web References: https://doi.org/10.1038/s43247-025-02652-z
References: DOI: 10.1038/s43247-025-02652-z
Image Credits: Pusan National University
Keywords: Climatology, Climate change, Climate variability, Ocean surface temperature, Monsoons, Weather forecasting, Ocean warming, Precipitation
