Maintenance of the mean kinetic energy in the global ocean by the barotropic and baroclinic energy routes: the roles of JEBAR and Ekman dynamics

Aiki, Hidenori; Richards, Kelvin J; Sakuma, Hirofumi

doi:10.1007/s10236-011-0382-y

Cited by 7 publications

(8 citation statements)

References 61 publications

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“…These positive signals indicate conversion of the mean APE to the mean KE, which is then dissipated by the boundary friction at the continental slope of the ocean. (See Aiki et al 2011b for the global distribution of the energy dissipation by the boundary friction in the 0.1…”

Section: A Model Diagnosis In Density Coordinatesmentioning

confidence: 99%

Energetics of the Global Ocean: The Role of Mesoscale Eddies

Aiki

Zhai

Greatbatch

2015

World Scientific Series on Asia-Pacific Weather and Climate

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This article reviews the energy cycle of the global ocean circulation, focusing on the role of baroclinic mesoscale eddies. Two of the important effects of mesoscale eddies are: (i) the flattening of the slope of large-scale isopycnal surfaces by the eddy-induced overturning circulation, the basis for the Gent-McWilliams parametrization; and (ii) the vertical redistribution of the momentum of basic geostrophic currents by the eddy-induced form stress (the residual effect of pressure perturbations), the basis for the Greatbatch-Lamb parametrization. While only point (i) can be explained using the classical Lorenz energy diagram, both (i) and (ii) can be explained using the modified energy diagram of Bleck as in the following energy cycle. Wind forcing provides an input to the mean KE, which is then transferred to the available potential energy (APE) of the large-scale field by the wind-induced Ekman flow. Subsequently, the APE is extracted by the eddy-induced overturning circulation to feed the mean KE, indicating the enhancement of the vertical shear of the basic current. Meanwhile, the vertical shear of the basic current is relaxed by the eddy-induced form stress, taking the mean KE to endow the eddy field with an energy cascade. The above energy cycle is useful for understanding the dynamics of the Antarctic Circumpolar Current. On the other hand, while the source of the eddy field energy has become clearer, identifying the sink and flux of the eddy field energy in both physical and spectral space remains major challenges of present-day oceanography. A recent study using a combination of models, satellite altimetry, and climatological hydrographic data shows that the western boundary acts as a "graveyard" for the westward-propagating eddies.

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Section: A Model Diagnosis In Density Coordinatesmentioning

confidence: 99%

Energetics of the Global Ocean: The Role of Mesoscale Eddies

Aiki

Zhai

Greatbatch

2015

World Scientific Series on Asia-Pacific Weather and Climate

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“…The barotropic and baroclinic components of U are defined by U bt ≡ Udz / H and U bc ≡ U − U bt , respectively. Then the kinetic energy (KE) in each vertical column can be separated into H ∣ U bt ∣ 2 (barotropic KE) and ∣ U bc ∣ 2 + ∣ w ∣ 2 dz (baroclinic KE) where H [ x ] is the bottom depth [ Holland , 1975; Baines , 1982; Cummins and Oey , 1997; Niwa and Hibiya , 2004; Carter et al , 2008; Aiki et al , 2011]. For simplicity we do not separate ∣ w ∣ 2 into barotropic and baroclinic component as our numerical results indicate that ∣ w ∣ 2 is 2 orders of magnitude smaller than the other kinetic energy terms and hence insignificant.…”

Section: Energy Diagnosismentioning

confidence: 99%

“…is the bottom depth [Holland, 1975;Baines, 1982;Cummins and Oey, 1997;Niwa and Hibiya, 2004;Carter et al, 2008;Aiki et al, 2011]. For simplicity we do not separate |w| 2 into barotropic and baroclinic component as our numerical results indicate that |w| 2 is 2 orders of magnitude smaller than the other kinetic energy terms and hence insignificant.…”

Section: Energy Diagnosismentioning

confidence: 99%

Modeling and energetics of tidally generated wave trains in the Lombok Strait: Impact of the Indonesian Throughflow

Aiki¹,

Matthews²,

Lamb³

2011

J. Geophys. Res.

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[1] This study investigates the possible impact of the Indonesian Throughflow (ITF) on tidally generated internal waves in Lombok Strait and examines the energetics of these disturbances. Using a two-dimensional nonhydrostatic numerical model which takes into account the variable width of the strait region, two main experiments have been performed, one without and one with an idealized ITF component in the upper layer flowing southward toward the Indian Ocean. These correspond to conditions in boreal winter and summer, respectively. Both experiments show trains of internal solitary-like gravity waves (ISWs). Overall, ISWs are more numerous on the north side of the sill where the narrower channel in effect amplifies the disturbances. In both experiments about 3.9 GW of energy is injected into barotropic and baroclinic tidal currents, of which about 2.6 GW is radiated away by internal gravity waves. The ITF regulates the way that the radiated energy is partitioned between the two sides of the sill. Without the ITF (boreal winter), the northward radiated energy flux is greater in magnitude than that radiated to the south. However, when the ITF is present (boreal summer), the northward radiated energy flux is smaller in magnitude than that radiated to the south. This result is obtained by diagnosing the flux of the Montgomery potential which can take into account the effect of finite amplitude waves and also offers a simple and robust energy diagnosis in the presence of time mean flows. Citation: Aiki, H., J. P. Matthews, and K. G. Lamb (2011), Modeling and energetics of tidally generated wave trains in the Lombok Strait:

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“…(2) the generation and conversion rates between gravitational potential energy and kinetic energy, as was done by Oort et al (1994) using observations; (3) the mean kinetic energy and gravitational potential energy, as was done by Aiki et al (2011) using a 1/10°global ocean model; (4) the Lorenz oceanic energy cycle, as was done by von Storch et al (2012) using a 1/10°global ocean model; or (5) the kinetic plus available potential energy budget, as was done by Hogg et al (2013) using an idealized 1/4°ocean model that mimicked the Atlantic Ocean. The conversion of kinetic energy to potential energy involves work done by several processes, some of which include horizontal pressure gradients, vertical velocities that result from the convergence or divergence of both the barotropic and baroclinic components of the horizontal velocities, and Reynolds stresses that are mediated by eddy kinetic 1 They made use of the Deep Water Archive and Buoy Group Archive.…”

Section: Introductionmentioning

confidence: 99%

Impact of parameterized lee wave drag on the energy budget of an eddying global ocean model

et al. 2013

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The impact of parameterized topographic internal lee wave drag on the input and output terms in the total mechanical energy budget of a hybrid coordinate high-resolution global ocean general circulation model forced by winds and air-sea buoyancy fluxes is examined here. Wave drag, which parameterizes the generation of internal lee waves arising from geostrophic flow impinging upon rough topography, is included in the prognostic model, ensuring that abyssal currents and stratification in the model are affected by the wave drag. An inline mechanical (kinetic plus gravitational potential) energy budget including four dissipative terms (parameterized topographic internal lee wave drag, quadratic bottom boundary layer drag, vertical eddy viscosity, and horizontal eddy viscosity) demonstrates that wave drag dissipates less energy in the model than a diagnostic (offline) estimate would suggest, due to reductions in both the abyssal currents and stratification. The equator experiences the largest reduction in energy dissipation associated with wave drag in inline versus offline estimates. Quadratic bottom drag is the energy sink most affected globally by the presence of wave drag in the model; other energy sinks are substantially affected locally, but not in their global integrals. It is suggested that wave drag cannot be mimicked by artificially increasing the quadratic bottom drag because the energy dissipation rates associated with bottom drag are not spatially correlated with those associated with wave drag where the latter are small. Additionally, in contrast to bottom drag, wave drag is a non-local energy sink. All four aforementioned dissipative terms contribute substantially to the total energy dissipation rate of about one terawatt. The partial time derivative of potential energy (non-zero since the isopycnal depths have a long adjustment time), the surface advective fluxes of potential energy, the rate of change of potential energy due to diffusive mass fluxes, and the conversion between internal energy and potential energy also play a non-negligible role in the total mechanical energy budget. Reasons for the <10% total mechanical energy budget imbalance are discussed.

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Maintenance of the mean kinetic energy in the global ocean by the barotropic and baroclinic energy routes: the roles of JEBAR and Ekman dynamics

Cited by 7 publications

References 61 publications

Energetics of the Global Ocean: The Role of Mesoscale Eddies

Energetics of the Global Ocean: The Role of Mesoscale Eddies

Modeling and energetics of tidally generated wave trains in the Lombok Strait: Impact of the Indonesian Throughflow

Impact of parameterized lee wave drag on the energy budget of an eddying global ocean model

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