Influence of Coriolis Parameter Variation on Langmuir Turbulence in the Ocean Upper Mixed Layer with Large Eddy Simulation

Abstract

Langmuir turbulence is a complex turbulent process in the ocean upper mixed layer. The Coriolis parameter has an important effect on Langmuir turbulence through the Coriolis-Stokes force and Ekman effect, however, this effect on Langmuir turbulence has not been systematically investigated. Here, the impact of the Coriolis parameter on Langmuir turbulence with a change of latitude (LAT) from 20°N to 80°N is studied using a non-hydrostatic large eddy simulation model under an ideal condition. The results show that the ratio of the upper mixed layer depth to Ekman depth scale (RME) RME = 0.266 (LAT = 50°N) is a key value (latitude) for the modulation effect of the Coriolis parameter on the mean and turbulent statistics of Langmuir turbulence. It is found that the rate of change of the sea surface temperature, upper mixed layer depth, entrainment flux, crosswind velocity, downwind vertical momentum flux, and turbulent kinetic energy budget terms associated with Langmuir turbulence are more evident at RME ⩽ 0.266 (LAT ⩽ 50°N) than at RME ⩾ 0.266 (LAT ⩾ 50°N). However, the rate of change of the depth-averaged crosswind vertical momentum flux does not have a clear variation between RME ⩽ 0.266 and RME ⩾ 0.266. The complex changes of both Langmuir turbulence characteristics and influence of Langmuir turbulence on the upper mixed layer with latitude presented here may provide more information for further improving Langmuir turbulence parameterization.

摘要

在海洋上混合层中,郎缪尔湍流是一个复杂的湍流过程。科里奥利参量通过科里奥利-斯托克斯强迫和埃克曼作用对郎缪尔湍流有着重要的影响。然而,随着纬度的变化,科里奥利参量对郎缪尔湍流的影响变化目前尚未进行系统探究。本文在理想情况下,将纬度从20oN变化到80oN,采用非静力近似的湍流大涡模拟模式,探究了科里奥利参量的变化对郎缪尔湍流的影响。结果表明科里奥利参量对郎缪尔湍流的平均和湍流统计参量的调制作用,在上混合层深度与埃克曼深度尺度比值RME = 0.266(latitude = 50oN)时,存在着关键的改变。在RME ≤ 0.266(latitude ≤ 50oN)情况下海表温度、上混合层深度、夹卷通量、垂直于风方向的速度、沿着风方向的垂向动量通量和湍动能收支项的变化率要比在RME ≥ 0.266(latitude ≥50oN)情况下要更加显著。然而,深度平均的沿着风方向的垂向动量通量随着RME的变化没有显著改变。郎缪尔湍流和郎缪尔湍流对上混层的影响,随着纬度变化存在着复杂变化的研究成果,能够为更进一步提高郎缪尔湍流的参数化提供更多重要信息。