Cross-and Downstream Variability of Static Stability in the Gulf Stream

Abstract

The spatial distribution of static stability in the Gulf Stream was studied using cross-and downstream XBT sections taken between Cape Hatteras and 70°W. The cross-stream sections revealed large variations in static stability, even over small spatial scales (?10 km). In the downstream direction, following isopycnal Swallow floats, changes occur more gradually and are clearly correlated with the curvature of the float trajectory. With curvature effects removed, the residual down-stream or Lagrangian variance is just 15% of that in the cross-stream direction. The variability of the cross-stream sections which sample different water parcels, compared to that of the downstream sections which follow a single parcel, suggests that the balance of the constituent terms of potential vorticity varies from one fluid parcel to another, reflecting their different origins.