Validating and understanding the ENSO simulation in two coupled climate models

A newly developed Atmospheric General Circulation Model (AGCM) at T62 spectral truncation with 28 terrain-following (sigma = p/p(s)) levels coupled to the Modular Ocean Model version 3.0 (MOM3.0) is evaluated for its simulation of El Nino and the Southern Oscillation (ENSO). It is also compared with an older version of the AGCM coupled to the same ocean model. A dozen features of ENSO are validated. These characteristics of ENSO highlight its influence on global climate at seasonal to interannual scales. The major improvements of the ENSO simulation from this new coupled climate model are the seasonal phase locking of the ENSO variability to a realistic annual cycle of the eastern equatorial Pacific Ocean, the duration of the ENSO events and its evolution that is comparable to the ocean data assimilation. The two apparent drawbacks of this new model are its relatively weak ENSO variability and the presence of erroneous split ITCZ. The improvement of the ENSO simulation in the new coupled model is attributed to realistic thermocline variability and wind stress simulation.