Mixing in the western equatorial Pacific and its modulation by ENSO

Richards, Kelvin J; Kashino, Yuji; Natarov, Andrei; Firing, Eric

doi:10.1029/2011gl050439

Cited by 35 publications

(45 citation statements)

References 34 publications

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“…There are distinct differences between cruises with regard to the level of turbulence activity and the associated vertical diffusion coefficient, but in all cases there is a general decrease with depth in both ϵ and κ v down to ∼200 m. This depth corresponds approximately to the bottom of the thermocline (defined loosely as the maximum depth at which N 2 falls below ∼2 × 10 −4 s −2 ) which is in general around 200–250 m depth [see e.g., Richards et al ., , Figure 3]. At greater depths, three out of four of the cruise averages show distinct maxima in both ϵ and κ v [see also Richards et al ., , Figure 2b]. These elevated values at depth are restricted to profiles taken within less than 2 degrees of the equator and may be associated with the near‐equator elevated values estimated from Argo data by Whalen et al .…”

Section: Resultsmentioning

confidence: 99%

“…As pointed out by Richards et al . [], the turbulence activity within and above the thermocline tends to be associated with flow structures with relatively small vertical scale (we will refer to these flow features as SVSs), rather than the larger scale currents in the region. The cruise average vertical shear spectra

Φ_{u}

and

Φ_{v}

for the zonal ( u ) and meridional ( v ) components of velocity, respectively, in the depth interval 100–250 m are shown in variance preserving form in Figure .…”

Section: Resultsmentioning

confidence: 99%

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Shear‐generated turbulence in the equatorial Pacific produced by small vertical scale flow features

et al. 2015

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We investigate the characteristics of shear-generated turbulence in the natural environment by considering data from a number of cruises in the western equatorial Pacific. In this region, the vertical shear of the flow is dominated by flow structures that have a relatively small vertical scale of O(10 m). Combining data from all cruises, we find a strong relationship between the turbulent dissipation rate, , vertical shear, S, and buoyancy frequency, N. Examination of at a fixed value of Richardson number, Ri 5 N 2 =S 2 , shows that / u 2 t N for a wide range of values of N, where u t is an appropriate velocity scale which we assume to be the horizontal velocity scale of the turbulence. The implied vertical length scale, ' v 5 u t =N, is consistent with theoretical and numerical studies of stratified turbulence. Such behavior is found for Ri < 0.4. The vertical diffusion coefficient then scales as j v / u 2 t =N at a fixed value of Richardson number. The amplitude of is found to increase with decreasing Ri, but only modestly, and certainly less dramatically than suggested by some parameterization schemes. Provided the shear generating the turbulence is resolved, our results point to a way to parameterize the unresolved turbulence.

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Section: Resultsmentioning

confidence: 99%

Φ_{u}

and

Φ_{v}

for the zonal ( u ) and meridional ( v ) components of velocity, respectively, in the depth interval 100–250 m are shown in variance preserving form in Figure .…”

Section: Resultsmentioning

confidence: 99%

Shear‐generated turbulence in the equatorial Pacific produced by small vertical scale flow features

et al. 2015

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“…Strong turbulent mixing occurs within the strong shear zone where the Richardson number is low (Kanari et al, ; Peters et al, ). Turbulent mixing within and above the thermocline is also modulated by El Niño‐Southern Oscillation events, with the level of turbulent mixing being significantly greater during La Niña events (Richards et al, ). Most of these studies indicated that strong diapycnal mixing mainly occurs within the surface mixed layer and near the top of the thermocline, while the main thermocline is dominated by weak diapycnal mixing.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Diapycnal Mixing Between Water Masses in the Western Equatorial Pacific

Liang

Shang

et al. 2019

JGR Oceans

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Diapycnal mixing of momentum and heat is crucially important to ocean dynamics, as it affects the state of the ocean and its interactions with the atmosphere. For realistic climate and circulation predictions, the magnitude and distribution of diapycnal mixing must be accurately represented in ocean models. Based on full-depth microstructure data obtained in the western equatorial Pacific, we demonstrate that there is an enhanced diapycnal diffusivity layer nested below the thermocline of the western equatorial Pacific. Diapycnal diffusivities in this layer range from 5×10 −6 to 5× 10 −4 m 2 s −1 , one to two orders of magnitude higher than those predicted by the wave-wave interaction theory (5 ×10 −7 −5×10 −6 m 2 s −1 ). These enhanced diapycnal mixings are strongly related to the South Pacific Tropical Water intrusion. Stratification is largely weakened by the South Pacific Tropical Water intrusion; thus, the shear can easily trigger shear instabilities and induce strong diapycnal mixing. This enhanced diapycnal diffusivity layer occupies the water column between~250 and 750 m and spans from the equator to 10°N. Such widespread enhanced diapycnal mixing related to water mass intrusions may play an important role in the dynamics of the equatorial ocean, and it should be taken into account in ocean models. Plain Language SummaryThe Pacific is the largest ocean in the world and plays an important role in the global climate change. For example, it affects the typhoons, rainfall, and monsoon, which clearly affects human activities. To accurately predict the ocean circulation and climate, it is needed to understand the dynamic mechanism of the ocean, especially the turbulent mixing that changes the properties of sea water and drives the ocean circulation. In this study, we investigated the turbulent mixing between water masses with observation. We found that there is a layer of enhanced turbulent mixing with a thickness of approximately 500 m in the western equatorial Pacific. This strong turbulent mixing layer was strongly related to the water mass intrusion. Understanding the impact of the water mass on the turbulent mixing can provide references for ocean models and improve their prediction of the climate and circulation.

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“…Natarov & Richards, ). In situ observations, such as high‐resolution profiles of the horizontal velocity and kinetic energy dissipation rate, suggest that levels of mixing are indeed correlated with the levels of SVS activity, at least at depths above 300 m in the western equatorial Pacific Ocean (Richards et al, , ) and elsewhere in the equatorial ocean (cf. Gregg et al, ; Moum et al, ).…”

Section: Introductionmentioning

confidence: 99%

Enhanced Energy Dissipation in the Equatorial Pycnocline by Wind‐Induced Internal Wave Activity

Natarov

Richards

2019

JGR Oceans

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Numerical experiments show that in a zonally symmetric model of a tropical ocean forced only by transient winds both inertia‐gravity wave activity and the energy dissipation rate have a pronounced maximum in the pycnocline close to the equator regardless of the latitudinal distribution of the energy input into the ocean's mixed layer. We consider a number of factors that determine the spatial distribution of mixing and find that equatorial enhancement is due to a combination of three factors: a stronger superinertial component of the wind forcing close to the equator, wave action convergence at turning latitudes for equatorially trapped waves, and nonlinear wave‐wave interactions between equatorially trapped waves. The most important factor is wave action convergence at turning latitudes.

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Mixing in the western equatorial Pacific and its modulation by ENSO

Cited by 35 publications

References 34 publications

Shear‐generated turbulence in the equatorial Pacific produced by small vertical scale flow features

Shear‐generated turbulence in the equatorial Pacific produced by small vertical scale flow features

Enhanced Diapycnal Mixing Between Water Masses in the Western Equatorial Pacific

Enhanced Energy Dissipation in the Equatorial Pycnocline by Wind‐Induced Internal Wave Activity

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