SYNTHESIZING THE GULF-STREAM THERMAL STRUCTURE FROM XBT DATA

Thirty-six XBT temperature profiles have been used in a parametric mod el introduced by Hendry to model the Gulf Stream's thermal structure a t 65 degrees W between 200 and 1200 dbar, with an rms residual error o f 0.56 degrees C. Velocity has been computed geostrophically relative to 1200 dbar, and has been included in calculating potential vorticity analytically from the model. The resulting potential vorticity sectio n for 65 degrees W has been compared with the analogous result from He ndry's parametric model at 59 degrees W, as well as observed potential vorticity sections from 68 degrees to 55 degrees W. There is a signif icant feature in the potential vorticity structure at 65 degrees W not found at 59 degrees W-namely, a relative minimum in potential vortici ty along isopycnals, centered at the Gulf Stream's axis and 350 dbar. The modeled potential vorticity sections are consistent with the obser vations, including the downstream disappearance of this feature. The d ynamical implications of these results are briefly discussed.