ENSO in a Flux-Adjusted Coupled GCM

FLOR is a high-resolution coupled GCM -- recently developed by the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) -- that is now contributing routine real-time monthly predictions of global seasonal-to-interannual climate as part of the North American Multi-Model Ensemble (NMME). Although it has demonstrated improved skill at simulating and predicting the El Niño/Southern Oscillation (ENSO) and its impacts, several biases remain in FLOR's simulations of tropical Pacific climate. Toward understanding and mitigating those biases, we present results from experiments in which the model's climatological SST, surface wind stress, and surface salinity are corrected toward observations. The flux-adjusted model (FLOR-FA) shows striking improvements in some aspects of ENSO, including the magnitude of equatorial SST anomalies and their seasonal synchronization to the end of the calendar year. Other aspects, such as the short ENSO period, overly-westward SST anomaly propagation, and westward-displaced extratropical teleconnections, are not improved by the flux adjustment. The reasons for these changes are illuminated through analysis of the dominant ENSO feedbacks. The flux adjustments also prove useful for revealing inherent climatological biases in the component models -- such as an overly deep equatorial Pacific thermocline, that was previously obscured due to a compensating bias in the off-equatorial climatological wind stress curl in the unadjusted coupled model. The implications of these results for improving models, assessing the future of ENSO under climate change, and forecasting ENSO are discussed.