Influence of the North Atlantic Oscillation on the Heat Budget of the Mixed Layer in the North Atlantic

A. B. Polonskii and P. A. Sukhonos

The heat budget components that are involved in the formation of the tripole structure of the upper mixed layer (UML) temperature anomalies in the North Atlantic under the influence of the North Atlantic Oscillation (NAO) are analyzed using ORA-S3 oceanic reanalysis data for the winter period in 1959–2011. It is shown that the negative UML temperature anomaly in the western part of the tropical zone during the NAO intensification is mainly due to the anomalies of horizontal heat advection and eddy heat diffusion (i.e., nonlocal factors), as well as due to anomalous heat fluxes on the ocean surface (although with a lower significance level). Antiphase changes in the UML temperature in the eastern part of the tropical zone and in the western part of the subtropical zone are accompanied by the anomalies of the heat budget components of the opposite sign. In the subpolar zone, the anomalies of nonlocal components of heat budget also make significant contribution to the UML temperature variation which is in-phase with the one in the tropics. In the high-latitude areas of deep convection, the anomalous heat fluxes at the UML base are also important, and in the eastern part of the subpolar gyre,the anomalies of the net heat fluxes on the ocean surface are crucial too. The signs of the anomalies of the UML heat budget components forming the UML temperature fields in the North Atlantic during the periods with high and low values of the NAO index are opposite.