Decadal Variability of Atlantic Meridional Overturning Circulation (AMOC) Simulated with FGOALS-s2 Model

Decadal variability of Atlantic Meridional Overturning Circulation (AMOC) has been studied in the Flexible Global Ocean-Atmosphere-Land System model, version s2 (FGOALS-s2) preindustrial simulation. Traditionally, the streamfunction on depth coordinate is used to represent AMOC. According to correlations between the AMOC index on density coordinate at 49.5°N and AMOC index at all latitudes north of 34°S, the authors find that AMOC variations propagate southward from the deep-water formation region. Furthermore, the AMOC variability on density coordinate is larger at high latitudes North Atlantic than at low latitudes North Atlantic and South Atlantic. Moreover, the AMOC displays a low-frequency variability with a period of about 70 years. The low-frequency oscillation is related to the interactions between temperature and salinity variations that are associated with the AMOC variations and surface winds. The physics of this decadal variability is as follows. Surface winds in the Greenland-Iceland-Norwegian (GIN) seas are anomalously strong, leading to abnormally large evaporation and thus the positive sea surface salinity (SSS) anomalies. The SSS anomalies strengthen the convection in the GIN seas and subsequently intensify the AMOC. This leads to a strengthened northward heat transport and decreases the meridional temperature gradient and surface winds, which completes the phase reversal.