Langmuir circulation

When a steady wind blows across a water surface, it transfers momentum to the water. The resulting circulation can organize into long, roughly parallel cells whose axes lie broadly along the wind direction. In a cross-section, neighboring cells rotate in opposite directions. Where surface flows converge, water and buoyant material can collect; between convergence zones, surface divergence is associated with upward motion from below. The alternating bands of convergence and divergence form the visible pattern often called windrows.

Foam, floating algae, and other buoyant material may accumulate in the convergence bands, making Langmuir circulation visible as streaks on otherwise open water. The circulation also moves water vertically: downwelling can carry surface material below the surface, while upwelling brings deeper water upward in adjacent zones. Its scale and strength vary with wind and wave conditions, so the pattern is not always easy to see.

The phenomenon is named for Irving Langmuir, who documented parallel surface streaks and proposed an explanation after observing floating seaweed in the Sargasso Sea and later studying similar patterns in Lake George, New York. Fridtjof Nansen's earlier observations of Arctic sea ice drifting at an angle to the wind also informed the subsequent study of wind-driven water motion.