Observed growth of Langmuir circulation

摘要: Surface velocity patterns and upper ocean density profiles are presented from a period following sudden increase in wind. A prior wind speed of 8 m/s failed to produce visible signs Langmuir circulation. After the increased 13 m/s, circulation developed within 15 min. The initial scale observed was about 16 m, streak streak, may have been restricted by depth measurements. This spacing is two thirds dominant wavelength (4-s-period waves). (two cell widths) at roughly 40 m/h for next hour. measurements indicate mixing which over same rate 20 m/h; thus vertical horizontal aspect ratio 1:1. Prior stratification weak (buoyancy frequency 1.5 cph), probably did not affect initially. Mixing surface oceans important wide variety concerns, including global climate health marine life. Two main causes this can be identified: (1) when water cooled, it becomes denser sinks, downward either bottom or until limited preexisting stratification; (2) mechanically stir layer some depth, usually stratification. former result considerable depths, but latter occurs more often, majority world oceans. Frequently, driving forces occur together. What details mixing? For example, bubbles dragged deep into mixed layer, injecting gases depth? Are there repeatable features could lead improved models its effects? When blows water, lines often on surface, running parallel In an exemplary series experiments, [1938] found these convergence along with downwelling below each line. He also that maxima downwind currents lines. Thus organized rolls alternating sign, aligned wind, parcels follow helical paths downwind. form layers has come called “Langmuir circulation.” Historically, term implied any particular mechanism formation, generally used reference other similar structures (e.g., roll vortices atmosphere wall-bounded convection). [1938, p. 123] expressed his belief “the set up apparently constitute essential epilimnion produced.” Clearly, “helical vortices” efficient transporting momentum, energy, matter throughout water. Three mechanisms currently considered drive An interaction between waves winddriven shear gives rise as linear instability. review theory, observations before 1983, given Leibovich [1983]. Even without waves, turbulent will due breakdown