Role of Parameterized Eddies in the Energy Budget of the Global Thermohaline Circulation: Cabbeling versus Restratification

L. Shogo Urakawa Center for Climate System Research, University of Tokyo, Chiba, Japan

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Hiroyasu Hasumi Center for Climate System Research, University of Tokyo, Chiba, Japan

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Abstract

The gravitational potential energy (GPE) budget of the global thermohaline circulation is investigated with a non-eddy-resolving model under a realistic configuration. The model incorporates parameterizations for mesoscale eddies and an equation of state that takes pressure dependency of density into account. Both vertical mixing and energy conversion from kinetic energy equally supply the GPE to the ocean, and its total amount is about 680 GW. Earlier studies point out that most of the GPE supplied by vertical mixing and energy conversion from kinetic energy is consumed by the cabbeling effect associated with the diabatic diffusion process. However, this study reveals that over 60% of the supplied GPE is adiabatically converted to eddy kinetic energy by the layer thickness diffusion and undergoes viscous dissipation, which is not resolved in the low-resolution model used here. Although the cabbeling effect on the GPE budget reduces in the presence of parameterizations of mesoscale eddies, its contribution is not necessarily negligible.

Corresponding author address: L. Shogo Urakawa, Center for Climate System Research, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8568, Japan. Email: surakawa@ccsr.u-tokyo.ac.jp

Abstract

The gravitational potential energy (GPE) budget of the global thermohaline circulation is investigated with a non-eddy-resolving model under a realistic configuration. The model incorporates parameterizations for mesoscale eddies and an equation of state that takes pressure dependency of density into account. Both vertical mixing and energy conversion from kinetic energy equally supply the GPE to the ocean, and its total amount is about 680 GW. Earlier studies point out that most of the GPE supplied by vertical mixing and energy conversion from kinetic energy is consumed by the cabbeling effect associated with the diabatic diffusion process. However, this study reveals that over 60% of the supplied GPE is adiabatically converted to eddy kinetic energy by the layer thickness diffusion and undergoes viscous dissipation, which is not resolved in the low-resolution model used here. Although the cabbeling effect on the GPE budget reduces in the presence of parameterizations of mesoscale eddies, its contribution is not necessarily negligible.

Corresponding author address: L. Shogo Urakawa, Center for Climate System Research, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8568, Japan. Email: surakawa@ccsr.u-tokyo.ac.jp

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