A Realization of Bias Correction Method in the GMAO Coupled System

Over the past several decades, a tremendous effort has been made to improve model performance in the simulation of the climate system. The cold or warm sea surface temperature (SST) bias in the tropics is still a problem common to most coupled ocean atmosphere general circulation models (CGCMs). The precipitation biases in CGCMs are also accompanied by SST and surface wind biases. The deficiencies and biases over the equatorial oceans through their influence on the Walker circulation likely contribute the precipitation biases over land surfaces. In this study, we introduce a bias correction method in the CGCM modeling to correct model biases. This approach utilizes the history of the model’s short-term forecasting errors and their seasonal dependence to modify model’s tendency term and to eliminate its climate drift. The fields u,v,T,p_s are then, in fact, adjusted towards the climate of the analyzed fields of the Modern-Era Retrospective Analysis for Research and Application-2 (MERRA-2) in the atmosphere of each model integration. The study shows that such an approach removes most of model biases, including the warm bias in the tropical SST and double–intertropical convergence zone (ITCZ) problem in the CGCM. A number of other aspects of the model simulation (e.g. extratropical transient activities) are also improved considerably due to the imposed pre-processed bias corrections. The impacts of this bias correction on the sub-seasonal to seasonal (S2S) predictions are also assessed in this study. Because many regional biases in the GEOS-5 CGCM are common amongst other current models, our approaches and findings are applicable to these other models as well.