ENSO diversity in the NCAR CCSM4 climate model

In this study we examine ENSO diversity in a 500 year control simulation of the National Center for Atmospheric Research (NCAR) Community Climate System Model version 4 (CCSM4), focusing on warm events. Standard and modified Nino3 and Nino4 indices are used to identify different event types. CCSM4 shows a rich diversity of El Nino flavors with characteristics that are comparable to what was found in observations, the SODA 2.0.2/3 ocean reanalysis, and the GFDL CM2.1 model, a climate model whose ENSO characteristics have been extensively analyzed. In agreement with previous studies available in the literature, warm events peaking in the central/western Pacific are characterized by wind stress and precipitation fields confined to the western side of the basin, and show weak or absent recharge/discharge thermocline processes. A heat budget analysis of four different El Nino flavors, peaking at different longitudes, confirms the leading role of the thermocline and zonal advective feedbacks in the Nino3 and Nino4 regions, respectively. However, the growth of events centered further west appears to be controlled by nonlinear zonal advection, a result that differs from what was found in the GFDL CM2.1 model, but that is consistent with some observational evidence.