New climate pattern discovered in the tropics may extend storm prediction weeks ahead

Researchers at the Institute of Science and Technology Austria (ISTA) have discovered a previously unknown cyclic pattern in the Earth’s tropical climate. The new phenomenon, called the tropics-wide intraseasonal oscillation (TWISO), repeats roughly every 30–60 days and influences rainfall, winds, and temperature across vast tropical regions.

The findings, published on November 24, in the Proceedings of the National Academy of Sciences (PNAS), mark one of the most significant advances in climate dynamics in recent years.

TWISO represents a system-wide “heartbeat” of the tropics, a coherent pulse in which multiple components of the atmosphere and ocean move in sync. This discovery helps explain variations in rainfall and temperature that occur on timescales shorter than El Niño but longer than everyday weather systems. By identifying the physical mechanism behind this oscillation, scientists have opened a new pathway for improving medium-range forecasts that could help predict tropical storms weeks in advance.

Until now, most large-scale oscillations known to affect the tropics, such as the El Niño–Southern Oscillation (ENSO), have occurred over months or years. TWISO bridges this gap, functioning on an intraseasonal scale of roughly one to two months. Researchers believe it could significantly improve forecasts for phenomena such as tropical cyclones, drought onset, and monsoon variability, all of which depend heavily on tropical energy and moisture cycles.

Caroline Muller, who leads the Geophysical Fluid Dynamics group at ISTA, says that the discovery shows how even well-studied climate regions can hide new patterns in plain sight. “It reminds us that the tropics, often seen as stable and repetitive, can still surprise us with fundamental dynamical behavior,” she explains.

The pulse of the tropical atmosphere

TWISO is driven by synchronized oscillations between the ocean and atmosphere. During each cycle, convection, temperature, radiation, and winds fluctuate together in an organized rhythm. At the surface, changes in sea surface temperature (SST) trigger shifts in convection over the so-called Indo-Pacific warm pool, a region where ocean temperatures remain around 30°C (86°F), the highest on the planet.

As convection strengthens over the warm pool, heat and moisture rise into the atmosphere, warming the free troposphere and intensifying the Hadley and Walker circulations. These vast overturning systems transport air north–south and east–west, distributing energy across the tropics. When the cycle peaks, stronger surface winds enhance evaporation and ocean cooling, causing the system to reverse.

Each TWISO phase acts like a pendulum swing. In its active phase, the tropics become warmer and wetter; in its suppressed phase, they turn cooler and drier. The cycle completes in about 45 days on average, corresponding to the period detected in both reanalysis and satellite data.

The effect is so large that it can alter the tropical mean state, slightly changing how much sunlight is reflected back to space and how heat moves from the equator to higher latitudes. Scientists call this the tropical energy pulse, an intrinsic oscillation of Earth’s climate system that helps regulate the planet’s thermal balance.

The science behind the discovery

The ISTA-led team identified TWISO by analyzing decades of meteorological data, combining satellite records with atmospheric reanalysis datasets. One of the primary tools was ERA5, the fifth-generation reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF).

This dataset integrates historical weather observations dating back to 1940, providing a global reconstruction of atmospheric conditions.

To confirm the signal, the team compared ERA5 results with data from NASA’s Clouds and the Earth’s Radiant Energy System (CERES), which measures radiation fluxes at the top of the atmosphere. Both datasets revealed the same striking pattern, consistent 30–60-day oscillations in tropical-mean temperature, surface winds, and radiation.

The discovery was not a coincidence but the result of high-resolution spectral analysis. By filtering out slower variations such as seasonal cycles and El Niño events, researchers exposed a rhythmic pulse hidden within the daily data. TWISO appeared in multiple independent variables, confirming that it represents a true physical process, not a statistical artifact.

Bao and his colleagues also found that the oscillation emerges even in periods when the well-known Madden–Jullian Oscillation (MJO) is inactive. This suggests that TWISO is a fundamental property of the tropical system, not merely a byproduct of existing modes like the MJO or ENSO.

How TWISO works

The discovery sheds light on the complex coupling between convection, radiation, and ocean heat exchange. TWISO begins when surface temperatures in the Indo-Pacific warm pool rise slightly, increasing the difference between the ocean and overlying air. This drives stronger heat fluxes upward, fueling deep convection and thunderstorm formation.

As convection intensifies, latent heat released by condensation warms the upper atmosphere, triggering a stronger large-scale circulation. This circulation increases wind speed at the surface, which enhances evaporation and cools the ocean. Over the next few weeks, this cooling suppresses convection, leading to a quieter atmospheric phase.

During each cycle, the system oscillates between these two energy states — one dominated by ocean heat input and the other by atmospheric cooling. In this way, TWISO acts as a natural regulator of tropical energy exchange.

The oscillation’s amplitude and timing also appear to influence regional weather. When TWISO enters its warm, active phase, conditions become more favorable for tropical cyclone formation, particularly in the western Pacific and Indian Ocean basins. During its cool, suppressed phase, the likelihood of storm development decreases.

What it means for weather prediction

Forecasting tropical weather remains one of climate science’s greatest challenges. While modern numerical models can predict storms up to ten days ahead, accuracy rapidly declines beyond two weeks. The newly identified TWISO offers a potential breakthrough by adding a predictable rhythm to the tropics within the 30 to 60-day range.

If forecasters can determine the current phase of TWISO, they may be able to estimate when the next surge of convection, and hence tropical cyclone activity, will occur. This would provide communities at risk with additional time to prepare for severe weather.

Improved prediction on these intraseasonal timescales would also benefit agriculture, water management, and disaster planning. In regions dependent on monsoon rains, such as South Asia, even a few extra weeks of reliable outlooks could make a critical difference for farmers and emergency planners.

However, Bao cautions that the exact effects of TWISO on regional climates remain uncertain. More work is needed to understand how it interacts with local factors such as ocean currents and land–sea contrasts. Future studies will test whether current climate models can reproduce the oscillation’s behavior, and if not, how model physics must evolve to capture it.

A new lens on the tropical engine of Earth’s climate

The identification of TWISO challenges a long-held assumption that the Hadley and Walker circulations remain steady on short timescales. Instead, they now appear to oscillate dynamically, shaping the global transfer of heat and moisture far more rapidly than previously thought.

This insight could also change how scientists view tropical–extratropical interactions. Variations in tropical energy balance can influence jet streams and storm tracks thousands of kilometers (miles) away, linking weather in the equatorial Pacific to that in North America or Europe.

TWISO’s discovery opens a new field of inquiry into tropical predictability and global climate coupling. It suggests that other hidden oscillations may exist, waiting to be found in the planet’s vast datasets. Understanding them will not only advance weather forecasting but also deepen our knowledge of how Earth’s climate engine breathes and maintains balance.

“By identifying TWISO, we’ve revealed a rhythm that has always been there, one that connects storms, rainfall, and energy across half the planet. It’s a heartbeat of the tropics that we can finally hear,” Bao said.

References:

¹ Hidden in Plain Sight – ISTA – November 24, 2025

² Tropics-wide intraseasonal oscillations – Jiawei Bao et al. – Earth, Atmospheric, and Planetary Sciences – November 24, 2025 – https://doi.org/10.1073/pnas.2511549122 – OPEN ACCESS

Reet Kaur

I’m a science journalist and researcher at The Watchers, contributing to the Epicenter edition, where I cover peer-reviewed scientific research and emerging discoveries across Earth and space sciences. With a background in astronomy and a passion for environmental science, I’ve worked in shark and coral conservation in Fiji, conducting reef and shark-behavior research, contributing to mangrove restoration, and earning PADI Open Water and Coral Reef Certifications. I bring a blend of scientific rigor and storytelling to illuminate the discoveries shaping our planet and beyond.

This author does not have any more posts.