Laboratory studies of wind‐driven Langmuir circulations

Abstract

Langmuir circulations in a wind wave tank have been observed and measured by a variety of methods including dye patterns and floating surface tracers. On the basis of measurements of cellular wavelength λc as a function of surface wavelength λw and depth H a tentative functional relation for the dependence of λc/H upon λw/H is proposed. The experiments clearly imply that the waves play an important role in the mechanism of formation of the Langmuir circulations but that the depth of the layer has a significant modifying influence. On the basis of certain ‘rake’ experiments and other indirect observations it is proposed that when λw/H < 1, the primary scale of Langmuir circulations, related to λw, transfers energy to a larger scale that is commensurate with the depth such that λc/H ≃ 2. Under these circumstances, two distinct scales of Langmuir circulations may exist simultaneously.

Observations and Theories of Langmuir Circulation: A Story of Mixing

“…At this point, Faller and Caponi (1978) undertook more laboratory studies and, in addition to introducing the terminology "CL-1" and "CL-2" for the first and second editions of the Craik-Leibovich analyses, showed that both mechanisms do, in fact, produce rolls in the laboratory.…”

Phytoplankton accumulation in Langmuir cells1

“…Their existence has been noted for some time (Langmuir 1938), and many explanations have been suggested (Scott et al 1969;Pollard 1977). The theory of gcnelmation by intersecting wave trains (Craik and Leibovich 1976) has received exp,?rimental support (Faller 1978;Faller and Caponi 1978). In this paper we sl-all ignore downwind transport and consider only movement in a vertical cro:;s-section perpendicular to the axis.…”

Secondary current properties generated by wind-induced water waves in experimental conditions

“…Matsunaga and Uzaki [16] visualized the streaky structure in a laboratory flume, in the same manner as Faller and Caponi [8], and pointed out that not a water wave but the flow instability may induce large scale circulation. In their experiments, the secondary currents were induced only by wind shear (i.e., no wave condition), implying that the CL2 model should be sufficiently examined.…”

“…The theory proposed by Craik and Leibovich [7] is called CL2, and has been supported by many researchers. Faller and Caponi [8] conducted laboratory experiments to visualize the streaky structure within a horizontal plane; they postulated the presence of circulation, and pointed out the relationship between streak spacing and wind speed. In the natural ocean, such streaky structures are often observed (see Thorpe's [9] in depth review).…”