The Atlantic Meridional Overturning Circulation, Atlantic Multi-Decadal Oscillation, and North Atlantic Oscillation in Three Climate System Models

Abstract

This study investigates Atlantic Meridional Overturning Circulation (AMOC), Atlantic Multi-decadal Oscillation (AMO), and wintertime North Atlantic Oscillation (NAO) simulated by Flexible Global Ocean–Atmosphere–Land System Models (FGOALS) including version 2 of the spectral model (FGOALS-s2) and fast version and version 2 of the grid-point model, FGOALS-gl and FGOALS-g2, respectively. The models can effectively capture the northward warm and salty sea water transport associated with the AMOC, NAO pressure dipole, and basin-wide sea surface temperature (SST) changes in the North Atlantic associated with AMO. AMOC strength is more realistically simulated by FGOALS-s2 than by the grid models. With the same external forcings, the behaviors of the NAO evolution are highly model-dependent, indicating the importance of climate natural variability. In the grid models, the maps of correlation between winter-mean sea level pressure (SLP) and the NAO index describe a mid-latitude positive center located at the North Atlantic, whereas the positive center in FGOALS-s2 extends eastward to the Mediterranean Sea. The upward trend of the AMO index is evident in the simulations after the 1970s. Moreover, possible relationships among the three indices are examined in this study.