Every few years, the dramatic cycles of El Niño-Southern Oscillation (ENSO) ripple across the Pacific Ocean, leaving profound imprints on the planet's weather. For South America, ENSO is more than a distant phenomenon; it is a powerful force that shapes rainfall patterns, triggers climate extremes, and alters ecosystems. But there’s a lesser-known player in this grand narrative: Low-Level Jets (LLJs), atmospheric wind currents that act as nature’s highways, transporting moisture across the continent and fueling weather extremes.

In our latest study, we revealed how ENSO and the Pacific Decadal Oscillation (PDO) work together to influence the activity of these LLJs in South America. Far from being passive players, these jets are critical drivers of precipitation extremes—flooding fields, swelling rivers, and intensifying storms from the Amazon Basin to Argentina’s agricultural heartlands. Understanding these mechanisms offers not only new scientific insights but also practical tools for preparing for and mitigating extreme weather events.

The Winds that Shape a Continent’s Weather

LLJs along the eastern Andes are vital atmospheric conduits, transporting vast amounts of moisture and heat across thousands of kilometers. In South America, these winds are shaped by the towering Andes and organized into three distinct types: the Central LLJ, Northern LLJ, and Andes LLJ. Each plays a critical role in defining the region’s weather, influencing where rain will fall—or where droughts will persist.

Our findings reveal that these winds are intricately tied to the rhythms of ENSO and PDO. During El Niño events, particularly when combined with a warm PDO, the Central LLJ intensifies, directing massive moisture flows toward southeastern South America. This dynamic often leads to extreme rainfall and devastating floods. On the other hand, La Niña years, under cold PDO conditions, strengthen the Northern and Andes LLJs, delivering heavy rains to the Amazon Basin and Andes foothills.

Decades of Data, Decoded

The relationship between ENSO, PDO, and LLJs is as complex as it is fascinating. To untangle this, we analyzed 65 years of atmospheric reanalysis data. Patterns began to emerge: while the Central LLJ has decreased in frequency over time, the Northern LLJ has grown more persistent and intense. These shifts hint at a fundamental rebalancing of South America’s climate dynamics, with significant implications for water security, agriculture, and biodiversity.

One of our most striking discoveries was how the alignment—or lack thereof—between ENSO and PDO phases acts like a climate “volume knob.” When El Niño coincides with a warm/neutral PDO, the Central LLJ ramps up, driving a sharp increase in extreme rainfall events in southeastern South America. Conversely, during La Niña and cold PDO, the Northern LLJ dominates, intensifying rainfall in the Amazon Basin.

Why This Matters

For millions of people across South America, these atmospheric patterns are not just theoretical—they are deeply personal. They determine crop yields, flood risks, and even livelihoods. Imagine a farmer in Argentina counting on predictable rains, only to face an unprecedented drought linked to shifting LLJ behavior. Or communities in the Amazon confronting escalating floods during La Niña years.

The stakes are high. As climate change continues to reshape global atmospheric systems, these dynamics are likely to intensify, leading to more frequent and severe precipitation extremes. Our findings underscore the importance of integrating these insights into early warning systems, disaster planning, and climate adaptation strategies.

The Road Ahead: A Call to Action

The journey to this study was marked by challenges, triumphs, and the collective effort of a dedicated team. Analyzing decades of data required patience and precision, but the rewards were worth it. Each discovery, from uncovering trends in LLJ activity to linking them to ENSO-PDO phases, brought us closer to understanding how nature’s most powerful systems interact.

This study raises urgent questions: How will climate warming further disrupt the delicate balance between ENSO, PDO, and LLJs? Will precipitation extremes become even more unpredictable, jeopardizing water and food security across South America? To answer these questions, we must advance climate modeling capabilities to capture the intricate interactions of atmospheric circulation and large-scale oceanic oscillations.

Understanding these systems isn’t just an academic pursuit—it’s a step toward resilience. By shedding light on the forces driving South America’s most extreme weather, we aim to empower communities, scientists, and policymakers to make informed decisions in the face of increasing climate uncertainty.