Numerical simulations of Atlantic meridional overturning circulation (AMOC) from OMIP experiments and its sensitivity to surface forcing

Atlantic meridional overturning circulation (AMOC) plays an important role in transporting heat meridionally in the Earth’s climate system and is also a key metrical tool to verify oceanic general circulation models. Two OMIP (Ocean Model Intercomparison Project phase 1 and 2) simulations with LICOM3 (version 3 of the LASG/IAP Climate System Ocean Model) developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics (IAP), are compared in this study. Both simulations well reproduce the fundamental characteristics of the AMOC, but the OMIP1 simulation shows a significantly stronger AMOC than the OMIP2 simulation. Because the LICOM3 configurations are identical between these two experiments, any differences between them must be attributed to the surface forcing data. Further analysis suggests that sea surface salinity (SSS) differences should be mainly responsible for the enhanced AMOC in the OMIP1 simulation, but sea surface temperature (SST) also play an unignorable role in modulating AMOC. In the North Atlantic, where deep convection occurs, the SSS in OMIP1 is more saline than that in OMIP1. We find that in the major region of deep convection, the change of SSS has more significant effect on density than the change of SST. As a result, the SSS was more saline than that in OMIP2, leading to stronger deep convection and subsequently intensify the AMOC. We conduct a series of numerical experiments with LICOM3, and the results confirmed that the changes in SSS have more significant effect on the strength of AMOC than the changes in SST.