Manuscript

Accurate replication of the processes associated with the energetics of the tropical ocean should be necessary if coupled GCMs are to simulate the physics of ENSO correctly. In particular, the energetics includes the transfer of energy from the winds to the ocean thermocline and energy dissipation during the ENSO cycle. Here, we analyze ocean energetics in coupled GCMs in terms of two integral parameters describing net energy loss in the system using the approach of Brown and Fedorov (2009). These parameters are (1) the efficiency γ of the conversion of wind power into the buoyancy power that directly affects the rate of change of the Available Potential Energy (APE) in the ocean and (2) the e-folding rate α that characterizes the damping of APE by turbulent diffusion and other processes. Estimating these two parameters for coupled models reveals significant deficiencies (and large differences) in how state-of-the-art coupled GCMs reproduce the ocean energetics as compared to ocean-only models and data assimilating models. The majority of the coupled models we analyzed show a lower efficiency (values of γ in the range of 10-50 % versus 50-60 % for ocean-only simulations or reanalysis) and too much energy damping (values of α−1 in the range 0.4-1 years versus 0.9-1.2 years). These differences in the model energetics appear to reflect differences in the simulated depth of the thermocline, the overall thermal structure of the tropical ocean, and the structure of ocean equatorial currents