Abstract
Diapycnal mixing affects the uptake of heat and carbon by the ocean as well as plays an important role in global ocean circulations and climate. In the thermocline, winds provide an important energy source for furnishing diapycnal mixing primarily through the generation of near-inertial internal waves. However, this contribution is largely missing in the current generation of climate models. In this study, it is found that mesoscale winds at scales of a few hundred kilometers account for more than 65% of near-inertial energy flux into the North Pacific basin and 55% of turbulent kinetic dissipation rate in the thermocline, suggesting their dominance in powering diapycnal mixing in the thermocline. Furthermore, a new parameterization of wind-driven diapycnal mixing in the ocean interior for climate models is proposed, which, for the first time, successfully captures both temporal and spatial variations of wind-driven diapycnal mixing in the thermocline. It is suggested that as mesoscale winds are not resolved by the climate models participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) due to insufficient resolutions, the diapycnal mixing is likely poorly represented, raising concerns about the accuracy and robustness of climate change simulations and projections.
Highlights
Diapycnal mixing in the ocean influences vertical transport of heat, dissolved gases, nutrients, and pollutants
To understand influences of mesoscale winds on near-inertial internal waves (NIWs) and diapycnal mixing, we analyze simulation results derived from a high-resolution coupled regional climate model (CRCM)[30]
We developed and tested a new parameterization (MFP) of wind-driven diapycnal mixing in ocean interior for climate models
Summary
Diapycnal mixing in the ocean influences vertical transport of heat, dissolved gases, nutrients, and pollutants. As a natural resonant frequency of flows on a rotating planet, near-inertial internal waves (NIWs) are efficiently forced by fluctuating wind stresses[9,10]. To the best of our knowledge, the elevated diapycnal mixing observed in the Kuroshio extension region has not been replicated by any state-of-the-art ocean or climate models even though various parameterization schemes have been applied[15,16,17,18,19,20,21,22,23]. This might be partly due to inadequacies in the parameterization schemes. We investigate the role of mesoscale winds in powering diapycnal mixing in the thermocline
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