North Atlantic Oceanic Decadal Variability in the Hadley Centre Coupled Model

Abstract

The Hadley Centre coupled model is used to investigate the relationship between the North Atlantic oscillation (NAO), Labrador Sea deep convection, and sea surface temperature variability. It is shown that the model is capable of simulating many features of the observed variability. In particular, the model reproduces the observed relationship between decadal variations in Labrador Sea convection and the NAO. It also has surface temperature anomalies that propagate along the path of the North Atlantic Current (NAC) with a timescale close to that of observed anomalies. A number of sensitivity experiments are performed with the coupled model to understand the underlying mechanisms. Simulations in which the Labrador Sea convection is artificially enhanced and surpressed illustrate a time-lagged impact on the NAC and therefore on sea surface temperature in that region. Further simulations with a sinusoidal forcing of convection confirm the role of Labrador Sea Water (LSW) in determining the timescale for propagation of the surface temperature anomalies. The timescale of surface anomalies moving along the path of the NAC is determined by the movement of LSW at intermediate depths.