In the tumultuous waters of the open ocean, an international constellation of satellites has documented an astonishing display of nature’s power, measuring an ocean wave reaching a height of nearly 20 meters. This observation, captured during a recent powerful storm, stands as one of the largest ever reliably measured from space and provides unprecedented insight into how the immense energy from ocean storms propagates across the globe. The findings underscore the critical role of space-based observation in understanding the complex dynamics of the sea and the far-reaching impacts of extreme weather events.
New research combining data from multiple advanced satellite missions has revealed that the most significant coastal threats often arrive long before a storm itself, or even from storms that never make landfall. These remote tempests generate powerful, long-period swells that travel thousands of kilometers as “storm messengers,” carrying destructive potential to distant shores. By tracking these swells from their genesis in a raging storm to their arrival at coastlines an ocean away, scientists are building a far more accurate and comprehensive picture of wave behavior, improving forecasting models and deepening the understanding of the planet’s intricate climate system.
A Record-Breaking Observation
The pivotal measurement was taken on December 21, 2024, at the peak of Storm Eddie, a cyclone that became the largest storm in terms of average wave height over the past decade. Data from the French–US Surface Water and Ocean Topography (SWOT) satellite confirmed the existence of waves averaging nearly 20 meters high, a scale comparable to the height of the Arc de Triomphe in Paris. This confirmation of such a massive wave in the open ocean provides a new benchmark for extreme sea states and validates the enhanced capabilities of modern satellite altimetry in capturing phenomena that are nearly impossible to measure directly with ships or buoys, which often do not survive such conditions.
The research, led by Fabrice Ardhuin of the Laboratory of Physical and Spatial Oceanography in France, focused not only on the sheer size of the waves within Storm Eddie but also on the subsequent journey of the energy it unleashed. The team’s analysis marked a significant step forward in oceanography, moving beyond static measurements to a dynamic tracking of a storm’s complete lifecycle and its global influence. This work was made possible by a synergistic approach, leveraging the unique strengths of several different satellite systems to create a cohesive, long-term dataset.
The Global Journey of a Swell
Perhaps more significant than the record wave height was the ability of scientists to track the storm’s resulting swell as it radiated across an astonishing 24,000 kilometers of ocean. The energy from Storm Eddie, which raged in the North Pacific, was monitored as it traveled through the Drake Passage and eventually reached the tropical Atlantic. This transoceanic journey, which unfolded between December 21, 2024, and January 6, 2025, illustrates how localized weather events can have planetary-scale consequences. Swells are long waves that carry a storm’s signature in their period—the time between successive crests. A long period, such as 20 seconds, indicates a powerful swell generated by a large and intense storm.
This capability to track swells provides critical information for coastal communities and maritime operations. While the storm itself may be thousands of kilometers away, the swells it generates can produce hazardous coastal conditions, including dangerous surf and coastal erosion, with little or no local warning signs. By understanding how these swells propagate, forecasters can provide more accurate and timely warnings for regions far removed from the storm’s immediate vicinity, improving safety and preparedness for coastal populations and a wide range of marine industries.
Advanced Tools of Oceanography
This comprehensive view of ocean dynamics is the result of integrating data from a new generation of satellites with a rich historical archive. The effort, funded by the European Space Agency’s Climate Change Initiative (CCI), merges decades of measurements from missions like SARAL, Jason-3, and the Copernicus Sentinels with the cutting-edge technology of the SWOT mission. This creates a continuous and detailed sea state record that stretches back to 1991.
The SWOT Satellite’s Unique Contribution
The SWOT satellite represents a technological leap forward. It combines traditional radar altimetry, which measures height at a single point, with wide-swath imaging capabilities. This allows it to measure not only the height of a swell but also its length and direction over a broad area. This directional information is crucial for pinpointing where waves originate and for understanding how their energy is distributed. SWOT’s precision is remarkable; it can detect swells as low as 3 centimeters and identify wavelengths up to 1,400 meters, capturing a spectrum of wave energy that other sensors often miss.
Long-Term Monitoring with Sentinel Missions
Complementing SWOT’s advanced capabilities is the ongoing work of missions like Copernicus Sentinel-6. Comprising two identical satellites, this mission serves as the current benchmark for tracking sea-level rise but also provides vital data for operational ocean forecasting. Sentinel-6 delivers near-real-time measurements of significant wave height and wind speed, which are fed directly into meteorological models. This data is invaluable for maritime safety, as it helps ship routers avoid dangerously high seas. As one project scientist noted, running a large tanker through waves of 8 to 10 meters is something to be avoided, and satellite data provides the necessary warning.
From Mythical Monsters to Measurable Threats
The recent findings build on decades of work that transformed “rogue waves”—once dismissed as maritime myth—into a scientifically accepted and studied phenomenon. For years, stories of impossibly large waves were treated as anecdotal, but data from earlier ESA satellites, such as ERS-1 and ERS-2, provided the first widespread, systematic proof of their existence. One study using this data identified more than ten individual giant waves exceeding 25 meters in height across the globe in a relatively short period.
The danger these waves pose is real and significant. In the last two decades, severe weather has been responsible for sinking over 200 large vessels, including supertankers and container ships, with rogue waves believed to be the primary cause in many instances. Famous encounters, such as the 29-meter wave that struck the Queen Elizabeth II cruise liner in 1995, brought public attention to the issue. The captain described it as “a great wall of water” that looked as if the ship were sailing into the White Cliffs of Dover. By providing robust, widespread data, satellites have made it possible to study the conditions that generate these extreme waves, paving the way for potential forecasting.
Refining the Physics of the Sea
The new generation of satellite data is not just confirming the existence of massive waves but is fundamentally improving the scientific models used to describe the ocean. The detailed measurements from SWOT revealed that the way energy is transferred within a storm is different than previously thought. Scientists discovered that short, steep waves inside the storm feed energy into the longer, more persistent swells. This nonlinear transfer allows seas to reach heights once considered impossible.
This deeper understanding has led to crucial corrections in wave modeling. One analysis based on data from a 2023 tropical cyclone found that previous energy calculations were overestimated by a factor of 20. The fuller picture provided by SWOT shows that while very long swells carry less energy than was assumed, more of that energy is concentrated in the dominant peak waves. These waves remain incredibly destructive, but their energy dynamics are now understood with much greater accuracy. This refinement of ocean physics will lead to better forecasts, increased maritime safety, and a more complete understanding of our planet’s powerful and dynamic oceans.
