We investigate the dynamics of interdecadal to centennial climate variability in the North Atlantic on the basis of a multicentury integration, which was conduceted with the CGCM ECHAM3/LSG. Our aim is to understand the physical mechanisms which generate longterm climate variability with preferred timescales deviating significantly from the red noise null hypothesis of climate variability.
A 35 year climate oscillation is identified in the North Atlantic, which can be understood in terms of the coupled air-sea mode concept. This mode involves interactions of the thermohaline circulation in the North Atlantic and atmospheric dynamics associated with the NAO. The generation of salinity anomalies plays a crucial role for the phase reversal. A characteristic feature of this mode is the pan-oceanic temperature synchronization between North Atlantic and North Pacific.
Furthermore the CGCM integration simulates a centennial climate oscillation in the North Atlantic with a period of about 180 years. This mode involves mainly atmosphere-ocean dynamics in the Nordic Seas. Slow adjustment processes of the subpolar gyre as well as changes of the meridional overturning provide the memory of this longterm oscillation. Changing wind patterns in the Nordic Seas turn out to be crucial for the phase reversal.
These results are discussed also in the light of a multicentury CGCM sensitivity experiment which supresses freshwaterflux effects on climate variaility