OBSERVATIONS OF GULF-STREAM MEANDER-INDUCED DISTURBANCES

Using moored array data collected across the Gulf Stream at 55 degrees W, the author has investigated the dynamical signatures of the veloci ty fluctuations at the thermocline (550 m) and near-bottom (4000 m) le vels. The cross-stream amplitude and phase structures for motions with period from 64 to 12 days, in a coordinate frame aligned with the ins tantaneous stream, have a striking resemblance to those computed from small amplitude instability theory. It is the sinuous or asymmetric mo de that appears to dominate the observed fluctuations as is predicted. In addition, the mean downstream velocity at the two levels is consis tent with a two-layer model for the mean now in which the lower layer has uniform potential vorticity. When fit to the data this model predi cts a value for the rate of change of the Coriolis parameter appropria te to this latitude, but one would expect it to be augmented by a fact or of 2 or so by the significant slope of the bottom in this region.