North Atlantic interdecadal variability: Oceanic response to the North Atlantic oscillation (1865-1997)

In contrast to the atmosphere, knowledge about interdecadal variability of the North Atlantic circulation is relatively restricted. It is the objectiv e of this study to contribute to understanding how the North Atlantic circu lation responds to a forcing by the North Atlantic oscillation (NAO) on int erdecadal timescales. For this purpose, the authors analyze observed atmosp heric and sea surface temperature (SST) data along with the response of an ocean general circulation model to a realistic monthly surface flux forcing that is solely associated with the NAO for the period 1865- 1997. In agreement with previous studies, it is shown that the relationship betwe en the local forcing by the NAO and observed SST anomalies on interdecadal timescales points toward the importance of oceanic dynamics in generating S ST anomalies. A comparison between observed and modeled SST anomalies revea ls that the model results can be used to assess interdecadal variability of the North Atlantic circulation. The observed/ modeled developments of interdecadal SST anomalies during the periods 1915- 39 and 1960-84 against the local damping influence from the NAO can be traced back to the lagged response (10- 20 yr) of the North Atla ntic thermohaline circulation and the subpolar gyre strength to interdecada l variability of the NAO. Additional sensitivity experiments suggest that p rimarily interdecadal variability in the surface net heat flux forcing asso ciated with the NAO governs interdecadal changes of the North Atlantic circ ulation.