Enhanced Turbulence Associated with the Diurnal Jet in the Ocean Surface Boundary Layer

Detailed observations of the diurnal jet, a surface intensification of the wind-driven current associated with the diurnal cycle of sea surface temperature (SST), were obtained during August and September 2012 in the subtropical Atlantic. Adiurnal increase in SST of 0.2 degrees to 0.5 degrees C was observed, which corresponded to a diurnal jet of 0.15 m s(-1). The increase in near-surface stratification limits the vertical diffusion of the wind stress, which in turn increases the near-surface shear. While the stratification decreased the turbulent dissipation rate epsilon below the depth of the diurnal jet, there was an observed increase in epsilon within the diurnal jet. The diurnal jet was observed to increase the near-surface shear by a factor of 5, which coincided with enhanced values of epsilon. The diurnal evolution of the Richardson number, which is an indicator of shear instability, is less than 1, suggesting that shear instability may contribute to near-surface turbulence. While the increased stratification due to the diurnal heating limits the depth of the momentum flux due to the wind, shear instability provides an additional source of turbulence that interacts with the enhanced shear of the diurnal jet to increase epsilon within this shallow layer.

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Sutherland Graig, Marie Louis, Reverdin Gilles, Christensen Kai H., Brostrtom Goran, Ward Brian (2016). Enhanced Turbulence Associated with the Diurnal Jet in the Ocean Surface Boundary Layer. Journal Of Physical Oceanography. 46 (10). 3051-3067. https://doi.org/10.1175/JPO-D-15-0172.1, https://archimer.ifremer.fr/doc/00358/46872/

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