Variability of the North-Atlantic wind-driven ocean circulation

A new approach to understand the physical processes that govern stability and internal variability of the large scale ocean circulation is outlined and current methods and results are reviewed. In this dynamical systems approach, variability is viewed as arising through successive bifurcations when parameters are changed. The potential of the approach is demonstrated through analyses of solutions of intermediate complexity models of the wind-driven ocean circulation. The analysis of the solution and bifurcation structure within a highly idealized and symmetric model shows the basic physical mechanisms at work behind the existence of multiple equilibria and temporal variability. Adding more realism to the models introduces imperfections to the idealized situations, and the modifications of the solution structure through the model hierarchy explains the origin of several phenomena in the most realistic models. The relevance of the results is discussed in relation to those of observations and of general circulation models.