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An international research team led by the Helmholtz-Zentrum Hereon has, for the first time, succeeded in visualizing and quantifying the complex airflow dynamics directly above the ocean surface in high resolution. Using an innovative laser measurement system, previously unknown and highly complex mechanisms of energy exchange between wind and waves have been deciphered鈥攁 significant step forward for climate research, weather models, and ocean dynamics. The research findings have been in Nature Communications.

The international team, led by Dr. Marc Buckley from the Hereon Institute of Coastal Ocean Dynamics, has achieved a breakthrough in high-resolution imaging of the ocean surface. Using a specially developed laser measurement system aboard the research platform FLIP (Floating Instrument Platform) in the Pacific Ocean, they were able to capture high-resolution images of airflow just a few millimeters to 1 meter above the ocean surface. They identified two wind-wave coupling mechanisms that occur simultaneously but act differently.

Short waves, about one meter in length, move slower than the wind. This causes a separation of the airflow: the wave crest blocks the wind, creating a pressure difference that transfers energy to the wave. Long waves, on the other hand鈥攗p to 100 meters in length鈥攎ove faster than the wind and generate different airflow patterns through their motion. These mechanisms operate simultaneously in different parts of the wave field鈥攁 crucial insight for advancing atmospheric and oceanic models.

Relevance for weather, climate, and marine biochemistry

The interactions between wind and waves are a central component of Earth's climate and weather systems. While it is largely accepted that these complex interactions control the exchange of energy, heat, and greenhouse gases between the atmosphere and the ocean鈥攁ffecting sea state, weather, and currents, the mechanisms remain, until today, largely unknown. The research team plans to further develop the system to also capture movements below the water surface with greater precision.

"Until now, no one has measured the airflow this close to the ocean surface, let alone mapped the mechanisms of energy exchange at such a fine scale," says lead author Buckley. "Our observations shed light on a physical frontier. This will enable us to advance the theoretical framework and develop more accurate descriptions of air-sea exchange processes, which have so far been only partially understood."

Unique imaging above the open ocean

The imagery is based on a laser that passes through both air and water: the green beam hits water droplets introduced into the air鈥攕imilar to mist illuminated by sunlight. These droplets follow the motion of the airflow, scatter the laser light, and make even the smallest movements in the air visible. At the same time, the laser penetrates the water surface. At the wind-driven surface, the light is refracted鈥攔evealing the structure of the water surface. This combination allows both the air and water sides to be visualized.

The method is based on Particle Image Velocimetry (PIV), an established technique in fluid dynamics. PIV provides precise information about flow structure and wind speeds. This marks the first time the technique has been used over the open ocean.