Assessment of fine-scale parameterizations at low latitudes of the North Pacific

Chang-Rong Liang,Xiao-Dong Shang,Ling-Hui Yu,Gui-Ying Chen,Yong-Feng Qi

doi:10.1038/s41598-018-28554-z

Chang-Rong Liang, Xiao-Dong Shang + Show 3 more

Open Access

https://doi.org/10.1038/s41598-018-28554-z

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Abstract

Fine-scale parameterizations based on shear and stratification are widely used to study the intensity and spatial distribution of turbulent diapycnal mixing in the ocean. Two well-known fine-scale parameterizations, Gregg–Henyey–Polzin (GHP) parameterization and MacKinnon–Gregg (MG) parameterization, are assessed with the full-depth microstructure data obtained in the North Pacific. The GHP parameterization commonly used in the open ocean succeeds in reproducing the dissipation rates over smooth topography but fails to predict the turbulence over rough topography. Failure of GHP parameterization over rough topography is attributed to the deviation of internal wave spectrum from the Garrett–Munk (GM) spectrum. The internal wave field over rough topography is characterized by energetic intermediate-scale and small-scale internal waves that are not described well by the GM model. The MG parameterization that is widely used in coastal environments is found to be successful in reproducing the dissipation rates over both smooth and rough topographies. The efficacy of GHP and MG parameterizations in evaluating the dissipation rates has been assessed. The result indicates that MG parameterization predicts the magnitude and variability of the dissipation rates better than the GHP parameterization.

Highlights

An outstanding question in oceanography is the intensity and spatial distribution of turbulent diapycnal mixing in the ocean
The smooth topography is defined as regions with topographic roughness (Tr) less than 105 m2, and the rough topography as that with value larger than 105 m2
Stations A1–A6 were located over smooth topography where values of Tr range from 103 to m2, and station A7 was located over rough topography where the value of Tr is 1.96 × m2 (Fig. 1b)

Summary

Introduction

An outstanding question in oceanography is the intensity and spatial distribution of turbulent diapycnal mixing in the ocean. The most commonly used fine-scale parameterization in the open ocean is the Gregg–Henyey–Polzin (GHP) parameterization[5,6,7] Studies relied on this parameterization[8,9,10,11,12,13,14] have shown that enhanced turbulent diapycnal mixing (κ ≥ 10−4 m2 s−1) occurs over rough topography. Enhanced diffusivities of O (10−4 m2 s−1) are found over rough topography in which topography interactions play an important role These studies based on GHP parameterization have greatly aided our knowledge of the intensity and distribution of turbulent diapycnal mixing in the open ocean. Using GHP parameterization near topographic features should be cautious and an appropriate fine-scale parameterization for regions where internal wave spectra deviate from GM spectra is needed to better understand the intensity and spatial distribution of turbulent diapycnal mixing. The assessment would provide a useful reference for researchers on choosing fine-scale parameterizations to explore the intensity and spatial distribution of turbulent diapycnal mixing in the open ocean

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