The Coupling between the Thermohaline Circulation and North Atlantic Oscillation in Global Ocean Atmosphere Land System Model

The thermohalion circulation, together with its atmospheric counterpart such as the Hadley Cell, constitutes the meridional circulation branch of the climate system. Long term integration with the Global Ocean-Atmosphere-Land System model (GOALS) of the Institute of Atmospheric Physics (IAP) has been used in the studies on the variability of the thermohaline circulation and its link to regional climate.

The contemporary thermohaline circulation is characterized as the Great Ocean Conveyor. It consists of cold, saline water sinking at high latitude of North Atlantic and then flow equator-ward at depth, upwelling throughout the world oceans, and returning as a northward flow of warm, salty water in the upper layers of the Atlantic Ocean. Preliminary verification shows that the coupled model is capable of simulating successfully not only the fundamental aspects of the thermohaline circulation (THC) but also an acceptable North Atlantic Oscillation in its atmospheric component. Analysis shows that the THC has irregular oscillations with a time scale of decades. When THC is stronger than normal, the pattern of SST anomaly appears as an anti-symmetric dipole mode, with a positive core over the sea southeast to the Newfoundland and a negative core in the domain west to the Northern African continent. Decadal variations appear to be more prominent within the subsurface than at sea surface. The strength of THC is negatively correlated with NAO index. Cross spectrum analysis shows that the evolution of THC and NAO is in phase in decadal scale variability. Further inspection shows that the typical anti-symmetric dipole mode of SST is dominated mainly by the THC, which is far different to the pattern of SST anomaly dominated by NAO.