Shipboard and satellite observations of upper ocean velocity and transport variability in the Gulf Stream

Abstract

Acoustic doppler velocities are combined with velocity profiles generated from XBT measurements to produce estimates of the flow field between Bermuda and the eastern coast of the United States. Repeated shipboard measurements along an ascending GEOSAT subtrack between Bermuda and Cape Cod allow study of rapid Gulf Stream Variability along the track, and comparison of sea surface and velocity measurements with those computed from the GEOSAT altimeter. The shipboard data were taken during two separate cruises on the R/V Oceanus in April and December, 1989. Using mass conservation constraints and inverse techniques, the transport across the Cape Cod Bermuda track has been balanced with transport across additional ship tracks between Bermuda and Cape Hatteras, and between Bermuda and Nova Scotia. The shipboard results show evidence of a rapid barotropic mode which caused changes in transport along the Cape Cod-Bermuda track on the order of 8 Sverdrups in a week period. Comparisons of sea surface velocity and dynamic height determined from the ship's data with measurements made from the GEOSAT altimeter showed a consistent picture of the Gulf Stream location and were also consistent in showing smaller scale variations in flow. The dynamic height difference across the Gulf Stream was approximately 10% higher for the GEOSAT measurements than for the shipboard measurements, which is within the expected errors of the analysis techniques.