Representation of the Equatorial Undercurrent in CMIP5 Models

The Equatorial Undercurrent (EUC) is a vital component of tropical Pacific circulation, helping to modulate the state of the equatorial Pacific Ocean. Here we compare the representation of the EUC in models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) with observations of the undercurrent. We find that the CMIP5 models consistently underestimate both the magnitude and variability of the EUC. Insufficient resolution as well as diffusivity parameterizations both contribute to a representation of the EUC that is too weak and too diffuse. Given the strong influence of the EUC on the evolution of tropical Pacific sea surface temperatures, model deficiencies in the EUC contribute to shortcomings in capturing ENSO dynamics and Pacific decadal variability. Further evaluation of the impact of EUC simulation on the climatology and variability in the tropical Pacific is necessary.