Overlooked Role of Mesoscale Winds in Powering Ocean Diapycnal Mixing

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.

An Improved Parameterization of Wind‐Driven Turbulent Vertical Mixing Based on an Eddy‐Resolving Climate Model

“…The turbulent vertical mixing is often regarded as the Achilles' heel of CGCMs. In this study, a MFP scheme (Jing et al, 2016) is incorporated into an eddy-resolving CESM to parameterize the wind-driven vertical mixing in the stratified ocean interior. The major conclusions are as follows: within the segment.…”

“…It has a horizontal resolution of 0.25° and 30 standard levels in the vertical. Such resolution is fine enough to resolve the atmospheric fronts and tropical cyclones that contribute substantially to I E W (Jing et al, 2016;Rimac et al, 2013). The ocean model is the Parallel Ocean Program version 2 (POP2; Danabasoglu et al, 2012;R.…”

“…In this study, the wind-driven vertical mixing is parameterized by implementing the MFP (Jing et al, 2016) into the CESM. In the MFP, the turbulent kinetic dissipation rate attributed to the NIWs is parameterized as…”

“…Such difficulties can be circumvented by parameterizing the wind-driven vertical mixing based directly on the model-simulated NIWs in the ocean interior, assuming that CGCMs provide a reliable simulation of both mesoscale eddies and NIWs. Jing et al (2016) relates the wind-driven vertical mixing to the on-site model-simulated NIW activity, with the downscale energy cascade to dissipation represented by a finescale parameterization (Polzin et al, 2014) modified to be accommodated to the underestimation of NIW shear variance by finite model vertical grid size. Offline application of this modified finescale parameterization (MFP) to an eddy-resolving regional ocean simulation reproduces the spatial and seasonal variations of wind-driven vertical mixing in the thermocline of North Pacific.…”

An Argo‐Derived Background Diffusivity Parameterization for Improved Ocean Simulations in the Tropical Pacific

“…Figure displays vertical diffusivity from single Argo profiles averaged over 250–2,000 m depth in the tropical Pacific Ocean. Low diffusivity mainly arises in the eastern tropical Pacific and the central equatorial Pacific; high diffusivity is found in the northwestern and southwestern tropical Pacific due to rough topography or elevated near‐inertial energy from wind (Alberty et al, ; Jing et al, ; Liu et al, ; Whalen et al, ). This pattern has been documented in the previous studies (Pollmann et al, ; Whalen et al, ).…”