Bias Corrections of the Heat Flux Damping Process to Improve the Simulation of ENSO Post-2000

Abstract

Around 2000, El Niño-Southern Oscillation (ENSO) began to experience weaker-intensity, but more frequent events (i.e., the increased central-Pacific (CP) ENSO), when a climate transition characterized by a La Niña-like mean state coincidently occurred. Associated with this climate shift, the ENSO simulation and prediction skills of most models in the 2000s were significantly lower than those in the 1980-90s, which had common biases that were amplified through this climate transition. In this work, a model bias is examined with the heat flux (HF)-sea surface temperature (SST) coupling processes over the tropical Pacific, which experienced coupling strength modification around 2000 over both the regions west and east of 160°W. A simple ENSO coupled model trained with the observations before 2000 is used to demonstrate that this model bias can be alleviated by updating the HF-SST coupling parameters. After updating these parameters, the performance of the ENSO model is significantly improved for reproducing observations over the tropical Pacific after the year 2000, suggesting the potential for a substantial improvement in ENSO simulation and prediction.