Response of the tropical Pacific to global warming from CGCM: Sensitivity to the performance of the upper ocean predictability
임보영; 노의근; 예상욱
Two coupled general circulation models (CGCMs), i.e., the Meteorological Research Institute (MRI) and Geophysical Fluid Dynamics Laboratory (GFDL) models, are chosen to examine changes in mixed layer depth (MLD) in the equatorial tropical Pacific with its relationship with ENSO under climate change projection. The control experiment uses pre-industrial greenhouse gas concentrations and the 2xCO2 experiment uses doubled CO2 levels. Changes in mean MLD due to atmospheric CO2 doubling are model dependent like changes in mean sea surface temperature (SST) and ENSO amplitude. The mean MLD becomes shallower about 20%~30% (MRI model) and 10%~20% (GFDL model) in the 2xCO2 experiment than that in the control experiment. In addition, changes in a relationship between the MLD and ENSO are quite different in the two CGCMs. One (i.e., MRI model) is significantly changed and the other (i.e., GFDL model) is not. While the anomalous MLD in the western and central equatorial Pacific is highly negatively correlated with ENSO in the control experiment, there is little systematic relationship in the 2xCO2 experiment for the MRI model. It is found that the anomalous zonal wind stress in the western and central equatorial Pacific, which is highly correlated with ENSO, that does not act effectively on the variability of anomalous MLD in the 2xCO2 experiment for the MRI model compared to the control experiment. We argued that two important factors (i.e., a relaxation of mean trade winds and an enhanced vertical stratification) are responsible for such changes. The implication is that under increased CO2 concentration the simulation of MLD is important to understand changes in mean SST and the ENSO response which depends on the MLD in the tropical Pacific.