DATE2026.02.19 #Press Releases

Uncovering the Key Mechanism Governing the Propagation of the Madden–Julian Oscillation, a Tropical Giant Cloud System That Influences Japan’s Weather

-Providing New Insights to Improve Subseasonal Weather Forecast Accuracy-

Summary

In the tropics, there exists a prominent atmospheric phenomenon known as the Madden–Julian Oscillation (MJO), in which massive clusters of cumulonimbus clouds—spanning several thousand kilometers from east to west—propagate eastward from the Indian Ocean to the Pacific Ocean. The MJO serves as a source of teleconnections that induce anomalous weather around the globe, and elucidating when and how its propagation occurs has long been one of the most critical challenges in tropical meteorology.

A research team led by Assistant Professor Daisuke Takasuka of the Graduate School of Science, Tohoku University, used a high-resolution atmospheric model capable of accurately simulating global cloud dynamics to generate an enormous ensemble of 4,000 “parallel worlds” for two MJO events. By examining how the MJO propagation is determined under identical external conditions, the team revealed key mechanisms governing its behavior.

The results show that in December, following the seasonal transition into winter, multiple MJO propagation scenarios coexist, leading to highly uncertain forecasts. The decisive factor in selecting among these scenarios was found to lie in subtle differences in tropical–midlatitude interactions, originating from variations in wind strength at the time of MJO initiation. These findings and the novel ensemble-based approach are expected to contribute to improved accuracy in seasonal forecasting and AI-based weather prediction.

This research was published in the scientific journal Science Advances on February 19, 2026, at 4 a.m. (JST)

Associate Professor Hiroaki Miura of the Department of Earth and Planetary Science also contributed to this study.

Figure：Conceptual illustration of the present study

Links

Tohoku University, RIKEN, JAMSTEC

Journals

Journal name	Science Advances
Title of paper	Propagation of the Madden–Julian Oscillation as a Deterministic Chaotic Phenomenon