On the diagnostics of AMOC variability in multi-centennial coupled climate simulations

The Atlantic Meridional Overturning Circulation (AMOC) variability in multi-centennial coupled climate simulations by CCSM3 and GFDL CM2.0 will be compared by applying a new diagnostic method that is different from the widely-used EOF analysis or composite method. Due to the lack of direct observations, the availability of multi-centennial or even millennial coupled climate simulations provides a unique tool to understand the long-term AMOC variability although the climate simulations has limitations in the representation of ocean eddies and other processes due to model resolution or other sources of uncertainties. The diagnostics of AMOC variability in coupled climate models has led to many insights about such as its vertical-meridional structures, its time scales, and its relationship with atmospheric variability. Here we will provide some new features about the modal transition, instability, and signal propagation of AMOC variability as well as the relation of the AMOC variability with the atmospheric mode North Atlantic Oscillation (NAO) in coupled CCSM3 and GFDL CM2.0 simulations. We will also provide the 3-dimensional structure of AMOC variability in these two models and compare the physical processes responsible for the differences in AMOC variability in the models.