Every winter, intense blasts of cold, dense air known as East Asian cold surges sweep southward from the Asian continent. While their severe impacts on East Asia are well documented, their journey often extends much further south into the Maritime Continent— the vast tropical archipelago region spanning Indonesia, Malaysia, the Philippines, and surrounding seas, located between the Indian and Pacific Oceans. This phenomenon has triggered several devastating floods in the region. However, exactly which areas get hit depends on the path the surge takes.
Some surges converge in the southern South China Sea, bringing heavy rainfall to western Borneo and the Malay Peninsula—for example, causing the catastrophic flood in January 2021. Other surges manage to cross the equator, triggering massive rainfall over northern Java, such as the devastating Jakarta flood in January 2020, which was recorded as one of the most extreme rainfall events in decades. This raises an important question: What determines the path of a cold surge in the Maritime Continent? Is it simply the initial strength of the surge, or is it controlled by other tropical variability across the region?
A new study published in Advances in Atmospheric Sciences by an Indonesian research team shows that a cold surge’s pathway is not solely driven by its intrinsic strength. Instead, it is strongly modulated by surrounding tropical variability. Key deciding factors are the pressure anomalies south of Indonesia. High-pressure anomalies in the south hinder the surge from crossing the equator, causing it to converge—and trigger rain—mostly north of the equator. On the other hand, low-pressure anomalies create a favorable pathway, allowing the surge to cross the equator and trigger heavy rain along the northern coast of Java. The sea surface temperature (SST) in the South China Sea also potentially influences this pathway. The study found that surges failing to cross the equator are generally preceded by warm SST anomalies, whereas those that flow into the Southern Hemisphere are preceded by cold anomalies.
"Our analysis reveals that a strong cold surge alone does not guarantee it will cross the equator — the surrounding tropical atmosphere and ocean act as gatekeepers," said lead author Narizka N. Purwadani, a PhD candidate at the Bandung Institute of Technology (ITB).
Through their analysis, the team found that several tropical atmospheric phenomena — including the Borneo Vortex, the Madden-Julian Oscillation, and Equatorial Rossby waves — essentially act as "gatekeepers" for these cold surge winds. Depending on their phase and positioning, these systems can either facilitate the cold surge's southward propagation into the Southern Hemisphere or hinder it from crossing the equator.
Uncovering these mechanisms is a major step forward, but it is just the beginning. According to the team, the ultimate goal is to significantly improve regional weather forecasting and early warning systems across the Maritime Continent. By integrating these atmospheric insights into weather prediction models, forecasters can better anticipate extreme rainfall and hydrometeorological disasters before they happen.
Moving forward, the team's next step is to run high-resolution atmospheric simulations to test exactly how changing sea surface temperatures affect these cold surge pathways. In a warming climate, understanding these air-sea interactions is vital to helping vulnerable communities protect themselves from extreme weather.
Advances in Atmospheric Sciences
Understanding the Cross-Equatorial Pathway: How Tropical Variability Modulates the Propagation of East Asian Cold Surges into the Southern Hemisphere
20-May-2026