FY 1997

Eddy-mean flow interaction in the Gulf Stream at 68°W: Part 2. Eddy forcing on the time-mean flow

Cronin, M.

J. Phys. Oceanogr., 26(10), 2132–2151, doi: 10.1175/1520-0485(1996)026<2132:EMFIIT>2.0.CO;2 (1996)

Data from the SYNOP 68°W current meter array show a trough pattern in the 26-month mean Gulf Stream path at 68°W and a cyclone in the mean deep flow. In order to determine whether eddies are controlling the speed and direction of the time-mean Gulf Stream flow at 68°W a theory is developed that extends the Eliassen-Palm theory for zonal-mean flows to time-mean flows. The eddy force is evaluated as the three-dimensional divergence of an eddy stress tensor and is equivalent to the eddy advection of momentum F_mom and the rotated divergent eddy stretching potential vorticity flux F_therm. The study region at 68°W is characterized by large amplitude trough formation events. It is shown that F_therm is associated with the growth stage of the eddy trough formation events and tends to turn the upper level time-mean flow southward into the trough pattern and accelerate and "spin up" the deep-layer cyclone. F_mom has a vertically coherent pattern associated with the decay stage of the trough formation events and tends to offset F_therm particularly in the deep layer.