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THE ENERGETICS OF THE GLOBAL OCEAN: THE IMPACT OF MODEL RESOLUTION AND DATA ASSIMILATION
JAMES RICHMAN, PATRICK HOGAN, PRASAD THOPPIL
Naval Research Laboratory
(Abstract received 12/20/2010 for session X)
ABSTRACT
We examine the energetics of a series of twin experiments using global Hybrid Coordinate Ocean Model (HYCOM) forced by the Navy Operational Global Atmospheric Forecast System (NOGAPS) and compare the model energetics with altimeter, surface drifter and deep current meter moorings. We use three simulations and a hindcast for our analysis, a multi-year global simulation at 1/12° resolution, a multi-year hindcast with the same 1/12° resolution model and data assimilation, a doubled resolution (1/25°) global model and a new 1/12° global model with tidal potential forcing in addition to the NOGAPS forcing. We find that the resolution of the present generation of ocean general circulation models of ~1/10° is inadequate to establish a vigorous abyssal circulation and the surface eddy kinetic energy (EKE) is only about 85% of the observed. Adding tidal forcing has a minimal impact on the surface circulation but increases the deep EKE by 12% and the kinetic energy of the mean flow (KEM) below 3000m by 25%. Doubling the horizontal resolution of the model increases the surface EKE to levels comparable to the drifter observations and increases the surface KEM by 40%, which is greater than the drifter estimates. The deep EKE and KEM also are increased to levels consistent with the deep current meters. Data assimilation increases the surface EKE to levels consistent with the drifter observations and increases the deep EKE and KEM. Surprisingly, data assimilation weakens the KEM at the surface and upper thermocline to levels below the 1/12° simulation. The increases in the surface EKE are dominated by the major current systems with the corresponding increases in the deep EKE below the surface EKE consistent with barotropic transfers of EKE from the surface to the deep by the enhanced surface eddy variability.
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2011 LOM Workshop, Miami, Florida February 7 - 9, 2011