TY - JOUR

T1 - Influence of langmuir circulation on the deepening of the wind-mixed layer

AU - Noh, Yign

AU - Goh, Gahyun

AU - Raasch, Siegfried

N1 - This work was supported by the National Research Foundation of Korea Grant funded by the Korean Government (MEST) (NRF-2009-C1AAA001- 0093068), by the Korean Ocean Research and Develop- ment Institute (KORDI) research program PE98512, and by the project ‘‘Research for the Meteorological Obser- vation Technology and Its Application’’ at the National Institute of Meteorological Research.

PY - 2011/3/1

Y1 - 2011/3/1

N2 - Analysis of large eddy simulation data reveals that Langmuir circulation (LC) induces a significant enhancement of the mixed layer deepening, only if the mixed layer depth (MLD) h is shallow and the buoyancy jump across it ΔB is small, when simulations are initiated by applying the wind stress to a motionless mixed layer with stratification. The difference in the entrainment rate between the cases with and without LC decreases with hΔB/υL2, where yL is the velocity scale of LC. The ratio of the mixing length scale l between the cases with and without LC is close to 1 for larger Rt [=(Nl0/q)2; Rt>~1], but it increases to above 10 with the decrease of Rt, where N is the Brunt-Väisälä frequency and q and l0 are the velocity and length scales of turbulence in the homogeneous layer. It is also found that, in the presence of LC, the effect of stratification on vertical mixing should be parameterized in terms of Rt instead of Ri (=(N/S)2), because velocity shear S is no longer a dominant source of turbulence. The parameterization is provided by l/l0=(1+αRt)-1/2 with α~50, regardless of the presence of LC. However, LC makes l0 much larger than conventionally used for the boundary layer.

AB - Analysis of large eddy simulation data reveals that Langmuir circulation (LC) induces a significant enhancement of the mixed layer deepening, only if the mixed layer depth (MLD) h is shallow and the buoyancy jump across it ΔB is small, when simulations are initiated by applying the wind stress to a motionless mixed layer with stratification. The difference in the entrainment rate between the cases with and without LC decreases with hΔB/υL2, where yL is the velocity scale of LC. The ratio of the mixing length scale l between the cases with and without LC is close to 1 for larger Rt [=(Nl0/q)2; Rt>~1], but it increases to above 10 with the decrease of Rt, where N is the Brunt-Väisälä frequency and q and l0 are the velocity and length scales of turbulence in the homogeneous layer. It is also found that, in the presence of LC, the effect of stratification on vertical mixing should be parameterized in terms of Rt instead of Ri (=(N/S)2), because velocity shear S is no longer a dominant source of turbulence. The parameterization is provided by l/l0=(1+αRt)-1/2 with α~50, regardless of the presence of LC. However, LC makes l0 much larger than conventionally used for the boundary layer.

KW - Large eddy simulation

KW - Mixed layer

KW - Oceanic mixed layer

UR - http://www.scopus.com/inward/record.url?scp=79954987534&partnerID=8YFLogxK

U2 - 10.1175/2010JPO4494.1

DO - 10.1175/2010JPO4494.1

M3 - Article

AN - SCOPUS:79954987534

VL - 41

SP - 472

EP - 484

JO - Journal of physical oceanography

JF - Journal of physical oceanography

SN - 0022-3670

IS - 3

ER -