North Atlantic oscillation and upper layer heat balance in the North Atlantic
The aim of the work is to identify the role of the North Atlantic Oscillation (NAO) in the formation of the interannual variability of the components of the closed upper mixed layer (UML) heat balance in the North Atlantic. The ORA-S3 oceanic reanalysis for the period 1959-2011 was used as the input data. It is confirmed that the NAO variability on a scale of 6-8 years is a coupled oscillation in the North Atlantic ocean-atmosphere system. The characteristic delay time of the ocean response to atmospheric forcing (interannual variation of NAO) is 24-28 months for the western parts of the subtropical and subpolar gyres. Changes of the heat balance components and the NAO index are predominantly in phase in the central and eastern parts of the subtropical gyre. The typical propagation speed of the oceanic signal in the UML from the western part of the subtropical gyre to the Iceland minimum area is 6-7 cm/s. The full cycle of the interaction of the NAO with anomalies of the UML heat balance components, taking into account the time of their advection, is about 6-8 years. The formation of a positive NAO phase in January is preceded (with temporal lags of about 25 months) by positive UML temperature anomalies in the Gulf Stream. In this case, a positive anomaly of partial derivative of the UML temperature occurs in the inner part of the subtropical gyre and East-Greenland current and a negative one - in the western part of the subtropical gyre. The formation of the negative NAO phase is preceded by conditions of the opposite nature.