Spring Mixing: Turbulence and Internal Waves during Restratification on the New England Shelf

MacKinnon, Jennifer A.; Gregg, Michael C.

doi:10.1175/jpo2821.1

Cited by 79 publications

(77 citation statements)

References 50 publications

(46 reference statements)

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“…4e). Richardson number Ri = N 2 /S 2 was estimated following MacKinnon and Gregg (2005). A 2 m buoyancy frequency and 16 m shear were used in the calculation.…”

Section: Water Mass Propertiesmentioning

confidence: 99%

Spatial distribution of turbulent mixing in the upper ocean of the South China Sea

2017

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Abstract. The spatial distribution of the dissipation rate (ε) and diapycnal diffusivity (κ) in the upper ocean of the South China Sea (SCS) is presented from a measurement program conducted from 26 April to 23 May 2010. In the vertical distribution, the dissipation rates below the surface mixed layer were predominantly high in the thermocline where shear and stratification were strong. In the regional distribution, high dissipation rates and diapycnal diffusivities were observed in the region to the west of the Luzon Strait, with an average dissipation rate and diapycnal diffusivity of 8.3 × 10 −9 W kg −1 and 2.7 × 10 −5 m 2 s −1 , respectively, almost 1 order of magnitude higher than those in the central and southern SCS. In the region to the west of the Luzon Strait, the water column was characterized by strong shear and weak stratification. Elevated dissipation rates (ε > 10 −7 W kg −1 ) and diapycnal diffusivities (κ > 10 −4 m 2 s −1 ), induced by shear instability, occurred in the water column. In the central and southern SCS, the water column was characterized by strong stratification and weak shear and the turbulent mixing was weak. Internal waves and internal tides generated near the Luzon Strait are expected to make a dominant contribution to the strong turbulent mixing and shear in the region to the west of the Luzon Strait. The observed dissipation rates were found to scale positively with the shear and stratification, which were consistent with the MacKinnon-Gregg model used for the continental shelf but different from the Gregg-Henyey scaling used for the open ocean.

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“…4e). Richardson number Ri = N 2 /S 2 was estimated following MacKinnon and Gregg (2005). A 2 m buoyancy frequency and 16 m shear were used in the calculation.…”

Section: Water Mass Propertiesmentioning

confidence: 99%

Spatial distribution of turbulent mixing in the upper ocean of the South China Sea

2017

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“…More detail measurements are required before establishing a reliable parameterization. Numerous formulas which are partly empirical or based on dynamic models have been proposed to relate turbulent dissipation rate, stratification, shear, or Richardson number (Price et al 1986;Polzin 1996;MacKinnon and Gregg 2005b) by dimensional scaling. Since the measurements described in MacKinnon and Gregg (2005a) are very similar with our situation in this paper, the parameterization method given by MacKinnon and Gregg (2005a) is used to compare with our observed data.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…The data indicated that the mixing was coherent at the 95 % confidence level with both shear and stratification which were coincident with the high winds. MacKinnon and Gregg (2005b) reported that the largest turbulent dissipation away from boundaries was coincident with shear from lower-mode near-inertial waves generated by passing storms. They also argued that turbulent dissipation rates increased with both shear and stratification which is also confirmed by the measurements observed in the Baltic Sea (van der Lee and Umlauf 2011); this differs from Gregg-Henyey scaling (Gregg 1989) used for the open ocean.…”

Section: Introductionmentioning

confidence: 99%

“…Cuypers et al (2013) observed a marked increase of heating rate due to enhanced mixing in the thermocline and interior ocean which was generated by storms. However, comparatively little work has been focused on turbulent dissipation related with near-inertial waves in coastal regions under high wind conditions (MacKinnon and Gregg 2005b). The main reason for this lack of information is that direct observations of turbulent energy dissipation are sparse.…”

Section: Introductionmentioning

confidence: 99%

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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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“…The analysis of the generation of the inertial oscillations and their dissipation was performed on the basis of turbulent dissipation rate ( ) and turbulent eddy diffusivity (k ρ ). These parameters were calculated by using the following formula (Mackinnon and Gregg, 2005;van der Lee and Umlauf, 2011;Palmer et al, 2008;Osborn, 1980):…”

Section: Methodsmentioning

confidence: 99%

Estimation of oceanic subsurface mixing under a severe cyclonic storm using a coupled atmosphere–ocean–wave model

2018

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Abstract. A coupled atmosphere-ocean-wave model was used to examine mixing in the upper-oceanic layers under the influence of a very severe cyclonic storm Phailin over the Bay of Bengal (BoB) during 10-14 October 2013. The coupled model was found to improve the sea surface temperature over the uncoupled model. Model simulations highlight the prominent role of cyclone-induced near-inertial oscillations in subsurface mixing up to the thermocline depth. The inertial mixing introduced by the cyclone played a central role in the deepening of the thermocline and mixed layer depth by 40 and 15 m, respectively. For the first time over the BoB, a detailed analysis of inertial oscillation kinetic energy generation, propagation, and dissipation was carried out using an atmosphere-ocean-wave coupled model during a cyclone. A quantitative estimate of kinetic energy in the oceanic water column, its propagation, and its dissipation mechanisms were explained using the coupled atmosphere-ocean-wave model. The large shear generated by the inertial oscillations was found to overcome the stratification and initiate mixing at the base of the mixed layer. Greater mixing was found at the depths where the eddy kinetic diffusivity was large. The baroclinic current, holding a larger fraction of kinetic energy than the barotropic current, weakened rapidly after the passage of the cyclone. The shear induced by inertial oscillations was found to decrease rapidly with increasing depth below the thermocline. The dampening of the mixing process below the thermocline was explained through the enhanced dissipation rate of turbulent kinetic energy upon approaching the thermocline layer. The wave-current interaction and nonlinear wave-wave interaction were found to affect the process of downward mixing and cause the dissipation of inertial oscillations.

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Spring Mixing: Turbulence and Internal Waves during Restratification on the New England Shelf

Cited by 79 publications

References 50 publications

Spatial distribution of turbulent mixing in the upper ocean of the South China Sea

Spatial distribution of turbulent mixing in the upper ocean of the South China Sea

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

Estimation of oceanic subsurface mixing under a severe cyclonic storm using a coupled atmosphere–ocean–wave model

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