Schubert David M.

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David M.

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  • Technical Report
    Application of acoustic-doppler current profiler and expendable bathythermograph measurements to the study of the velocity structure and transport of the Gulf Stream
    (Woods Hole Oceanographic Institution, 1988-09) Joyce, Terrence M. ; Dunworth, Jane A. ; Schubert, David M. ; Stalcup, Marvel C. ; Barbour, R. Lorraine
    We have addressed the degree to which Acoustic-Doppler Current Profiler (ADCP) and expendable bathythermograph (XBT) data can provide quantitative measurements of the velocity structure and transport of the Gulf Stream. An algorithm has been used to generate salinity from temperature and depth using an historical Temperature/Salinity relation for the NW Atlantic . Results have been simulated using CTD data and comparing real and pseudo salinity files. Errors are typically less than 2 dynamic cm for the upper 800 rn out of a total signal of 80 cm (across the Gulf Stream). When combined with ADCP data for a near-surface reference velocity, transport errors in isopycnal layers are less than about 1 Sv (106 rn3 /s), as is the difference in total transport for the upper 800 rn between real and pseudo data . The method is capable of measuring the real variability of the Gulf Stream, and when combined with altimeter data, can provide estimates of the geoid slope with oceanic errors of a few parts in 108 over horizontal scales of 500 krn .
  • Technical Report
    Cruise summaries of Oceanus cruises 205, leg 8, and 216
    (Woods Hole Oceanographic Institution, 1991-04) Joyce, Terrence M. ; Stalcup, Marvel C. ; Barbour, R. Lorraine ; Dunworth, Jane A. ; Schubert, David M.
    A study of the upper ocean thermal and density structure in the northwestern Atlantic in 1989 compared temperature and density measurements made with Expendable Bathythermograph (XBT) and Conductivity-Temperature-Depth instruments with current data from an acoustic Doppler current profiler and satellite infrared imagery and altimetry. Two cruises were made in the spring and winter of 1989 with the goal of directly measuring the upper ocean currents and variabilty of the Gulf Stream. The XBT observations were used to extend the measured velocities geostrophically from the near-surface region to depths of 750 meters, thereby allowing transport estimates to be made for the upper ocean. In April the measurments were compared and used with the GEOSAT altimeter which, unfortunately, was not operating during the December cruise.
  • Thesis
    Shipboard and satellite observations of upper ocean velocity and transport variability in the Gulf Stream
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1990-09) Schubert, David M.
    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.