North Atlantic Oscillation and Interannual Mixed-Layer Heat Balance Variability in the North Atlantic

The paper is devoted to the analysis of the interaction of the North Atlantic Oscillation (NAO) and the upper mixed layer (UML) in the North Atlantic using the ORA-S3 oceanic re-analysis data for the period 1959–2011s. A mechanism of the NAO maintaining at the interannual time scale has been specified. It is shown that the 6–8 yrs spectral peak in the NAO index time series is due to the interaction of the UML in the North Atlantic and the atmospheric boundary layer. It has been found that anomalies of the UML parameters generated by the NAO in the central and eastern parts of the North Atlantic reach its western part in 24–28 months. Due to advection and diffusion processes in the UML, the oceanic signal from the western part of the North Atlantic moves to the region of the Iceland Low and leads to change in the heat exchange between the ocean and the atmosphere and, hence, switch off the NAO phase. It is confirmed that the NAO variability at a scale of 6–8 years is a coupled mode in the North Atlantic ocean–atmosphere system.