A Comparison of Vessel-Mounted Acoustic Doppler Current Profiler and Satellite Altimeter Estimates of Sea Surface Height and Transports between New Jersey and Bermuda along the CMV Oleander Route

Abstract

Abstract In recent years the acoustic Doppler current profiler (ADCP) has found increasing use on commercial vessels to measure currents and their variability along selected routes in the ocean. One such dataset, in operation since late 1992, is the ADCP record from the Container Motor Vessel (CMV) Oleander, which operates between New Jersey and Bermuda. Because the Oleander ADCP system measures upper-ocean currents of O(10−2) m s−1 accuracy every 2.5 km, it provides excellent coverage of the mesoscale and submesoscale velocity field, and also of transport. The question addressed here is how well do estimates of fluxes between the continental shelf break and Bermuda compare with corresponding geostrophic estimates derived from satellite altimeter measurements of sea level extracted from weekly mapped fields along the same route. The Oleander route spans three distinct deep-sea regions: the Slope Sea, the Gulf Stream, and the Sargasso Sea. Agreement in sea surface height variability depends principally upon the length of the section being compared, and not upon eddy kinetic energy levels. Thus, yearly averages for short subsections such as across the quiet Slope Sea and energetic Gulf Stream both have correlation coefficients in excess of 0.9, whereas across the longer Sargasso Sea the correlation coefficient drops to 0.64 and to 0.58 for the 950-km-long Slope–Bermuda section. The principal cause of decrease in correlation with increasing distance appears to be due to ageostrophic flow, principally the Ekman layer and inertial motion, measured by the ADCP but not represented in the altimeter-derived geostrophic fluxes.