JEBAR, Bottom Pressure Torque, and Gulf Stream Separation

Abstract

A diagnostic, finite element, barotropic ocean model has been used to simulate the mean circulation in the North Atlantic. With the inclusion of the joint effect of baroclinicity and relief (JEBAR), the Gulf Stream is found to separate at the correct latitude, ?35°N, off Cape Hatteras. Results suggest that the JEBAR term in three key regions (offshore of the separation point in the path of the main jet, along the slope region of the North Atlantic Bight, and in the central Irminger Sea) is crucial in determining the separation point. The transport driven by the bottom pressure torque component of JEBAR dominates the solution, except in the subpolar gyre, and is also responsible for the separation of the Gulf Stream. Excluding high latitudes (in the deep-water formation regions) density variations in the upper 1000 m of the water column govern the generation of the necessary bottom pressure torque in our model. Examination of results from the World Ocean Circulation Experiment-Community Modelling Effort indicates that the bottom pressure torque component of JEBAR is underestimated by almost an order of magnitude, when compared to our diagnostic results. The reason for this is unclear but may be associated with the diffuse nature of the modeled thermocline in the CME as suggested by our model?s sensitivity to the density field above 1000 m.