Mixing in the Transition Layer during Two Storm Events

Dohan, Kathleen; Davis, Russ E.

doi:10.1175/2010jpo4253.1

Cited by 61 publications

(69 citation statements)

References 32 publications

(29 reference statements)

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“…The results documented in our study and those of other studies indicate that strong turbulent mixing occurs below the base of the mixed layer during the strong wind bursts (Grant and Belcher 2011;Dohan and Davis 2011). The magnitude of the enhanced mixing that is correlated with the near-inertial waves should be related to the energy flux that propagates from sea surface to the interior (Alford 2001).…”

Section: Introductionsupporting

confidence: 79%

Enhanced turbulent mixing induced by strong wind on the South China Sea shelf

Zhang

Tian

2014

Ocean Dynamics

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Integrated observations were made on the South China Sea shelf at 19°37' N, 112°04' E, under strong wind and heavy raining weather conditions in August 2005. Current data were obtained using a moored 150-kHz Acoustic Doppler Current Profiler, turbulent kinetic energy dissipation rate were measured with TurboMapII, and temperature was recorded by thermistor chains. Both the mixed layer thickness and the corresponding mean dissipation rate increased after the strong wind bursts. Average surface mixed layer thickness was 13.4 m pre-wind and 22.4 m post-wind, and the average turbulent dissipation rate in the mixed layer pre-wind and post-wind were 4.26 × 10 −7 and 1.09 × 10 −6 Wkg −1 , respectively. The post-wind dissipation rate was 2.5 times larger than the pre-wind dissipation rate in the interior layer and four times larger in the intermediate water column. Spectra and vertical mode analysis revealed that near-inertial motion post-wind, especially with high modes, was strengthened and propagated downward toward the intermediate layer. The ratio of post-wind high-mode energy to total horizontal kinetic energy increased below the surface mixed layer, which would have caused instabilities and result in turbulent mixing. Based on these data, we discuss a previous parameterization that relates dissipation rate, stratification, and shear variance calculated from baroclinic currents with high modes (higher than mode 1) which concentrate a large fraction of energy.

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Section: Introductionsupporting

confidence: 79%

Enhanced turbulent mixing induced by strong wind on the South China Sea shelf

Zhang

Tian

2014

Ocean Dynamics

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“…While large-scale entrainment mixing causes the mixed layer to deepen and cool over the course of several days without affecting the temperature below the mixed layer, diffusive mixing (term 4 on RHS of (1)) causes a transport of heat from the mixed layer to the waters below. Diffusive mixing thus can cause cooling within the mixed layer and warming below, thus reducing the stratification of the upper ocean (e.g., at Station Papa: Large et al, [1986]; Large and Crawford, [1995]; Dohan and Davis, [2011]). …”

Section: Methodology and Datamentioning

confidence: 99%

Estimating diffusivity from the mixed layer heat and salt balances in the North Pacific

et al. 2015

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Data from two National Oceanographic and Atmospheric Administration (NOAA) surface moorings in the North Pacific, in combination with data from satellite, Argo floats and glider (when available), are used to evaluate the residual diffusive flux of heat across the base of the mixed layer from the surface mixed layer heat budget. The diffusion coefficient (i.e., diffusivity) is then computed by dividing the diffusive flux by the temperature gradient in the 20 m transition layer just below the base of the mixed layer. At Station Papa in the NE Pacific subpolar gyre, this diffusivity is 1 × 10−4 m2/s during summer, increasing to ∼3 × 10−4 m2/s during fall. During late winter and early spring, diffusivity has large errors. At other times, diffusivity computed from the mixed layer salt budget at Papa correlate with those from the heat budget, giving confidence that the results are robust for all seasons except late winter‐early spring and can be used for other tracers. In comparison, at the Kuroshio Extension Observatory (KEO) in the NW Pacific subtropical recirculation gyre, somewhat larger diffusivities are found based upon the mixed layer heat budget: ∼ 3 × 10−4 m2/s during the warm season and more than an order of magnitude larger during the winter, although again, wintertime errors are large. These larger values at KEO appear to be due to the increased turbulence associated with the summertime typhoons, and weaker wintertime stratification.

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“…The shear production term PðS 2 Þ is less than the shear evolution @S 2 @t in the transition layer, but the phases of the two terms are in good agreement throughout the time series. Unidirectional monsoon winds disallow the resonance between rotation of the wind and earths rotation which is the cause of amplification of near-inertial currents in midlatitudes [Dohan and Davis, 2011]. In the Arabian sea, the time variation of wind stress and rotation of the bulk shear across the transition layer (Figure 9, fourth plot) cause the increase in magnitude of the bulk shear across the transition layer when this shear and wind stress are aligned.…”

Section: Journal Of Geophysical Research: Oceansmentioning

confidence: 99%

“…Several studies in the midlatitudes [Alford et al, 2012;Dohan and Davis, 2011] document the evolution of near inertial currents that are generated mostly by short-duration storms and by rotating winds. Alternatively, Weller et al [2014] found strong near-inertial currents generated by accelerating and decelerating wind stress in the unidirectional trade wind regime in the southeast Pacific.…”

Section: 1002/2014jc010198mentioning

confidence: 99%

Near‐inertial kinetic energy budget of the mixed layer and shear evolution in the transition layer in the Arabian Sea during the monsoons

et al. 2015

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We present the horizontal kinetic energy (KE) balance of near-inertial currents in the mixed layer and explain shear evolution in the transition layer using observations from a mooring at 15.268 N in the Arabian Sea during the southwest monsoon. The highly sheared and stratified transition layer at the mixed-layer base varies between 5 m and 35 m and correlates negatively with the wind stress. Results from the mixed layer near-inertial KE (NIKE) balance suggest that wind energy at times can energize the transition layer and at other times is fully utilized within the mixed layer. A simple two layer model is utilized to study the shear evolution in the transition layer and shown to match well with observations. The shear production in this model arises from alignment of wind stress and shear. Although the winds are unidirectional during the monsoon, the shear in the transition layer is predominantly near-inertial. The near-inertial shear bursts in the observations show the same phasing and magnitude at near-inertial frequencies as the wind-shear alignment term.

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Mixing in the Transition Layer during Two Storm Events

Cited by 61 publications

References 32 publications

Enhanced turbulent mixing induced by strong wind on the South China Sea shelf

Enhanced turbulent mixing induced by strong wind on the South China Sea shelf

Estimating diffusivity from the mixed layer heat and salt balances in the North Pacific

Near‐inertial kinetic energy budget of the mixed layer and shear evolution in the transition layer in the Arabian Sea during the monsoons

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