Australia: The Land Where Time Began

A biography of the Australian continent 

Southern Ocean - Routs of Energy Dissipation for Geostrophic Flows

At a global scale winds, heat fluxes and fresh water force circulation of the ocean. At much smaller scales  kinetic energy is dissipated in the turbulent layers and interior in the ocean (Wunsch & Ferrari, 2004; Hughes, Hogg & Griffiths, 2009), where the transport and storage of tracers such as heat and carbon dioxide is controlled by turbulent mixing (Sarmiento & Toggwieler, 1984; Sarmiento et al., 2004). In the Southern Ocean the primary input site of wind power is where the westerly winds align with the Antarctic Circumpolar Current (Wunsch, 1998), the potential energy created here being converted into a vigorous geostrophic eddy field through baroclinic instabilities. Mixing in the interior of the ocean can be powered by the eddy energy (Ferrari & Wunsch, 2009; Naviera Garabato et al., 2004; Nikurashin & Ferrari, 2011), though the mechanisms governing the transfer of energy to to the dissipation scale are poorly constrained. In this paper the authors1 present a simulation that simultaneously resolves meso-and submeso-scale motions as well as the topography-generated internal waves in the Southern Ocean. More than 80 % of the input wind power is converted from geostrophic eddies to smaller-scale motions in the abyssal ocean according to the simulation of the authors1 , the conversion being catalysed by rough, small-scale topography. About 20 % of the energy is radiated and dissipated away from topography in the ocean interior, where turbulent mixing can be sustained by it, though most of the energy is dissipated within the bottom 100 m of the ocean. The authors1 conclude that the turbulent mixing in the interior of the ocean would be diminished in the absence of rough topography.


Sources & Further reading

  1. Nikurashin, Maxim, Geoffrey K. Vallis, and Alistair Adcroft. "Routes to Energy Dissipation for Geostrophic Flows in the Southern Ocean." Nature Geosci 6, no. 1 (01//print 2013): 48-51.
Author: M. H. Monroe
Last updated 16/02/2013

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