Spatial and Temporal Structure of ENSO in 20th Century Climate Simulations

Tropical Paci c interannual variability is examined in nine state-of-the-art coupled climate models,and compared with observations and ocean analysis datasets,the primary focus being on the spatial structure and spectral characteristics of El Nio-Southern Oscillation (ENSO).To gain some insight in the underlying dynamics of interannual variability in the different models,the leading modes of thermocline variability are computed using an empirical orthogonal function approach.It is found that the spatial patterns of thermocline variability are qualitatively similar in all the models,and consistent with the recharge oscillator paradigm for ENSO.The meridional scale of the thermocline depth anomalies is generally narrower than observed,a result that can be related to the pattern of zonal wind stress perturbations in the central-western equatorial Paci c. The wind stress response to eastern equatorial Paci c SST anomalies in the models is narrower and displaced further west than observed.The meridional scale of the wind stress can affect the adjustment timescale of the equatorial thermocline,while the longitudinal location of the wind stress anomalies can in uence the advection of the mean zonal temperature gradient by the anom- alous zonal currents,a process that can promote the growth and longer duration of ENSO events when the wind stress perturbations are displaced eastwards.Thus,both discrepancies of the wind stress anomaly patterns in the coupled models with respect to observations may be responsible for the ENSO timescale being shorter in the models than in observations.The relative importance of anomalous zonal advection vs.mean vertical advection of temperature anomalies in the different models is also examined.