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Abstract:
Atlantic meridional overturning circulation (AMOC) plays an important role in Earth’s climate system and is also a key metric used 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 of these simulations reproduce the fundamental characteristics of the AMOC well, 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 surface shortwave radiation should be responsible for the enhanced AMOC in the OMIP1 simulation. In the Labrador Sea, a key region where deep convection occurs, shortwave radiation forcing in the OMIP1 experiment was 10-20 Wm-2 larger than that in OMIP2. As a result, the sea surface temperature (SST) was higher than that in OMIP2, leading to large evaporation and thus more saline sea surface salinity (SSS) in OMIP1. SSS anomalies strengthen convection in the Labrador Sea and subsequently intensify the AMOC. Finally, in this work, this process was confirmed by a sensitivity experiment with LICOM3.
