Monitoring Gulf Stream Transport by Radar Altimeter and Inverted Echo Sounders

Abstract

Profiles of the Gulf Stream sea surface height (SSH) from the Geosat altimeter were compared with thermocline depth measurements from inverted echo sounders (IES) for a period of about 19 months. The correlation between SSH anomalies and thermocline depth anomalies at about 68°W was 0.92. To distinguish between agreement in the location of the Gulf Stream jet and agreement in the strength of the jet, separate comparisons were made for jet location and the SSH difference across the Gulf Stream. Based on an error function fit to each Geosat and IES profile, the correlation between the jet centers from the two types of measurements was 0.97, and the correlation between the amplitudes of the error functions was 0.76. Although the altimeter measures surface geostrophic velocity, the high degree of vertical correlation in the Gulf Stream velocity profiles allows the altimeter to monitor transport fluctuations, as well as changes in jet position. Based on this assessment of the accuracy of the altimeter, the authors suggest that a correlation between the height difference across the Gulf Stream and the jet position between 48° and 65°W reflects large-scale changes in the structure of the recirculation gyres.