Potential Vorticity Balances and Horizontal Divergence along Particle Trajectories in Gulf Stream Meanders East of Cape Hatteras

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Abstract
Trajectories of 37 isopycnal RAFOS floats launched in the Gulf Stream off Cape Hatteras have been analyzed to examine the dynamics of meanders from a Lagrangian viewpoint. Using the float data in conjunction with information on the structure of horizontal velocity shear from the PEGASUS study (Halkin and Rossby), variations in planetary, curvature, and shear vorticity have been estimated along the float trajectories. Changes in fluid layer thickness were then inferred assuming potential vorticity is conserved following the floats. This analysis shows that curvature vorticity changes are typically 10%–20% of f (planetary vorticity) as fluid parcels travel between meander troughs and crests. Lateral shear changes on the order of 20%–30% of f are common as parcels move laterally relative to the jet axis between meander extrema. Although changes in these two terms are usually of opposite sign and tend to compensate, significant layer thickness changes do occur, with some parcels exhibiting 30% change... Abstract Trajectories of 37 isopycnal RAFOS floats launched in the Gulf Stream off Cape Hatteras have been analyzed to examine the dynamics of meanders from a Lagrangian viewpoint. Using the float data in conjunction with information on the structure of horizontal velocity shear from the PEGASUS study (Halkin and Rossby), variations in planetary, curvature, and shear vorticity have been estimated along the float trajectories. Changes in fluid layer thickness were then inferred assuming potential vorticity is conserved following the floats. This analysis shows that curvature vorticity changes are typically 10%–20% of f (planetary vorticity) as fluid parcels travel between meander troughs and crests. Lateral shear changes on the order of 20%–30% of f are common as parcels move laterally relative to the jet axis between meander extrema. Although changes in these two terms are usually of opposite sign and tend to compensate, significant layer thickness changes do occur, with some parcels exhibiting 30% change...

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