Impact of Tidal Current-Wind-Wave Obliquity on the Form and Orientation of Coastal Langmuir Circulations

Langmuir Circulation is a turbulent secondary flow, the product of non-linear interactions between surface waves and wind-driven shear imposed by the atmospheric surface layer. The circulations are observed as prominent counter-rotating cells. Langmuir Circulations affect the depth of the upper ocean mixed layer. In nature, realizations of perfect coalignment between the wind and wave fields are expected to the exception, not the norm, and it is thus relevant to assess how Langmuir turbulence responds to directional misalignment between the driving mechanisms responsible for their sustenance. Moreover, mean current directions - whether associated with tides or larger-scale eddies - show seasonal patterns while immediate local wind directions vary frequently. Thus, mean current-wind-wave parameter space, and the system response to variability in the underlying parameter space - affect form and orientation of Langmuir cells. Therefore, in this study, we investigate the affect of misaligned mean currents, wind, and wave fields on the structural and dynamical properties of coastal Langmuir turbulence (in this regime, bottom-boundary layer shear further alters the dynamics). We show that the misaligned mean current mechanistically changes the morphology of the Langmuir cells. Another observation of small-scale Langmuir structures reveals that packets of streaks at different horizontal planes align in different directions. This hints at the existence of a rotating small-scale Langmuir structures about the wall-normal axis forming a spiral, solely due to the interaction of misaligned wind-wave-mean current forcing.