Eddy convergence of heat, salt, density, and vorticity in the subtropical North Atlantic

Abstract

Profiles of absolute three-dimensional velocity at POLYMODE Array III Clusters A, B, and C are derived by vertically integrating the thermal wind relations and the first order vorticity equation. Horizontal reference velocities are set by using stable mean flows observed at 1500 m at Clusters A and B, and at 2500 m at Cluster C. The vertical reference velocity is Ekman pumping at the surface from published charts. The dot product of the resultant absolute profiles with the gradients of potential temperature, salinity, and potential density, gives profiles of turbulent convergence of the respective quantities. The implications that these velocity and convergence profiles have on North Atlantic water mass movements are discussed. While the relative velocity profile at Cluster B in identical to that published for a nearby area (using the β-spiral method), the reference velocity is more to the north. By referring to the profiles of turbulent convergence it is shown that the β-spinal method (which relies on finding the intersections of surfaces of constant potential density and potential vorticity, as well as their conservation) is ill-conditioned where conservation holds and physically unrealistic where it does not hold.