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How Are El Niño and La Niña Events Improved in an Eddy-Resolving Ocean General Circulation Model?

Abstract The present study compares the performance of two versions of the LASG/IAP (State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics/Institute of Atmospheric Physics) Climate System Ocean Model (LICOM) in reproducing the interannual variability associated with El Niño and La Niña events in the tropical Pacific. Both versions are forced with the identical boundary conditions from observed or reanalysis data, in which one version has a finer spatial resolution of (1/10)° in the horizontal domain and 55 vertical layers, and the other version has a coarse resolution of 1° in the horizontal domain and 30 vertical layers. ENSO simulations form the two versions are compared with observations and, in particular, the improvements with regard to ENSO by the finer resolution ocean model are emphasized. As a result of the finer spatial resolution, both the vertical temperature gradient and vertical velocity are better represented in the equatorial Pacific than they are by the coarse resolution model; and thus, the corresponding vertical advections of temperature are more reasonable. Besides the mean climatology, simulated ENSO events and relevant feedbacks are much improved in the finer resolution model. A heat budget analysis suggests that both thermocline feedback and Ekman feedback are mainly responsible for the rapid increase in temperature anomalies during the developing and mature phases of ENSO events.