Double Intertropical Convergence Zones in Coupled Ocean-Atmosphere Models: Progress in CMIP6

Reducing the double Intertropical Convergence Zone (ITCZ) bias has been the subject of intensive research in the climate modeling community. Recent studies have shown small to little progress in the ensemble of Coupled Model Intercomparison Project Phase 6 (CMIP6) models compared to Phase 3 (CMIP3) and Phase 5 (CMIP5) models in simulating the ITCZ. This study distinguishes the performances of the ensemble of CMIP models and the sub-ensemble of top five models in reference to the double ITCZ bias by using the spatial correlation as the metric. We show that while there was little progress in the whole CMIP6 ensemble, there is progress in the top five models from CMIP5 to CMIP6. These models have largely eliminated the bias. This improvement is masked in the whole ensemble by the larger inter-model spread. Results point to promising directions to which coupled models are heading to eradicate the chronic double ITCZ bias.