Langmuir circulation

Langmuir circulation

White streaks in this lagoon are due to the Langmuir circulation.

These lines of sargassum can stretch for miles along the surface. The clumps of floating algae are often concentrated by the strong winds and wave action associated with the Gulf Stream.

In physical oceanography, Langmuir circulation consists of a series of shallow, slow, counter-rotating vortices at the ocean's surface. These circulations are developed when a particular type of wind blows steadily over the sea surface. Irving Langmuir discovered this phenomenon after observing windrows of seaweed in the Sargasso Sea in 1927. Langmuir circulations usually circulate water with a depth of no more than 66 feet (20 m), which does not allow upwelling to bring nutrient-rich waters from the pycnocline – typically with a depth of more than 3,000 feet (900 m) – to the ocean surface.

The circulation was found to be 15° to the right of the wind in the northern hemisphere and the helix forming bands of divergence and convergence at the surface. At the convergence zones, there are commonly concentrations of floating seaweed, foam and debris along these bands. Along these divergent zones, the ocean surface is typically clear of debris since diverging currents force material out of this zone and into adjacent converging zones. On average, a particle in these vortices will complete a full revolution in one hour. At the surface the circulation will set a current from the divergence zone to the convergence zone and the spacing between these zones are of the order of 15–300 m (50–1,000 ft). Below convergence zones narrow jets of downward flow form and the magnitude of the current will be comparable to the horizontal flow. The downward propagation will typically be in the order of meters or tenths of meters and will not penetrate the pycnocline. The upwelling will generally be less intense and take place over a wider band under the divergence zone.

In an observation done at windspeeds of 14 m/s (46 ft/s) the horizontal spacing of the cells were 20 m (66 ft) and maximum vertical velocity was −18 cm/s (−7.1 in/s).^{[citation needed]}

External links

• Media related to Langmuir circulation at Wikimedia Commons