Langmuir Circulation


   Long, parallel streaks of floating debris or bubbles are sometimes observed when out on the Great Lakes.  These streaks are due to Langmuir circulation, which is generated by a continuous wind in relatively calm seas.  This type of circulation was first recognized in 1938 by Irving Langmuir, who observed such patterns of debris on the surface of the sea in the North Atlantic.  What happens is that in some instances the wind causes the formation of cells of rotating water that parallel the surface
(Figure 1).  Since two adjoining cells rotate in opposite directions, bands of convergent water associated with downwelling alternate with bands of divergent water associated with upwelling .  The dark blue areas on the front of the diagram show how parcels of water move through the cells.  The water diverted along the surface carries with it bubbles, foam, and debris (flotsam).  Since much of this material does not sink with the downwelling (converging) water, it accumulates to form a streak, which is what you see on the surface of the water.  Notice in Figure 1 that the wind blows parallel to the circulation cells and, therefore, the streaks.  Langmuir cells can be from several meters to many kilometers in length, and they typically do not reach over about six meters in depth.  Below the convection cells, the water remains relatively still.  Langmuir circulation can form quite quickly, and can last from several minutes to several hours.  Besides forming on the lakes such as the Great Lakes and the sea, sometimes Langmuir circulation cells also form on rivers.
 

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LIVING WITH THE GREAT LAKES
BROUGHT TO YOU BY:
GRAND VALLEY STATE UNIVERSITY
DEPARTMENT OF GEOLOGY
ALLENDALE, MICHIGAN 49401