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Analyzing energetics of the global ocean in density-coordinates
Hidenori Aiki and Kelvin J. Richards
University of Hawaii / JAMSTEC
(Abstract received 07/15/2007 for session X)
ABSTRACT
A set of 3-day snapshots from a high-resolution (0.1 deg) global OGCM simulation (Masumoto et al., 2004) were analyzed using a monthly-mean filter in density coordinates (80 layers), in order to demonstrate the self-consistency and utility of an adiabatic mean energy diagram which was introduced by Bleck (1985) and recently revisited by Iwasaki (2001) and Aiki and Yamagata (2006). The adiabatic mean energy diagram differs from the classical energy diagrams of Lorenz (1955) and Plumb (1983) in its use of modified definitions of the mean and eddy kinetic energies; these are given by the thickness-weighted mean velocity and the deviation from it, respectively, in density coordinates (Bleck, 1985; Iwasaki, 2001). The boundary condition of the adiabatic mean energy equations is robust and straightforward even in the presence of density surfaces intersecting (outcropping at) the top and bottom boundaries of the ocean, as recently shown by Aiki and Yamagata (2006). Understanding of the adiabatic mean energy diagram is fundamental to introducing the parameterization of the layer-thickness form drag (i.e. eddy form drag: residual effects of pressure perturbations) in OGCMs (Greatbatch, 1998). We show the global distribution of energy conversion done by the layer-thickness form drag, which is an energy cascade to the perturbation field whose rate is as intense as the works of the eddy-induced overturning circulations and the wind-induced Ekman transports in the world\'s oceans. The work associated with the vertical redistribution of momentum by the layer-thickness form drag is one order of magnitude larger than that associated with the horizontal redistribution of momentum. The layer-thickness form drag and the eddy-induced velocity are shown to be in near geostrophic balance.
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2007 LOM Workshop, Bergen, Norway, August 20-22, 2007