Generation of deep eddies by a turning baroclinic jet

Abstract

The North Atlantic Current (NAC) travels northward east of the Grand Banks until approximately 50°N where it makes a sharp turn to the east. Previous analysis of sea level variability in this region, known as the Northwest Corner, showed large-amplitude meandering and a quasi-regular production of anticyclonic eddies playing an important role in the air-sea heat exchange. Here we investigate key physical mechanisms of meandering of an idealized upper ocean turning jet using a two-layer model. The existing reduced-gravity thin jet theory is modified to take into account the crossjet velocity in the lower layer induced by the jet meanders. Such coupled system is capable to describe realistically baroclinic instability and to reduce the two-dimensional initial value problem to a rather simple one-dimensional formulation. Its linearized version is solved here to describe the fluid motion in both layers in terms of jet curvature. It is found that transient meander growth is enhanced in the vicinity of turning point owing to vertical coupling with deep eddies generated due to stretching in water column beneath growing meanders. Scaling for initial growth of deep cyclone–anticyclone pair is suggested based on a generalized thin jet theory. Patterns of further nonlinear evolution resembling observational data are described.