NAC

North Atlantic Current Experiment

Principal Investigators

D. Randolph Watts, Univ. of Rhode Island, Kingston, RI
R. Allyn Clarke, Bedford Institute of Oceanography, Dartmouth, Canada
Ross Hendry, Bedford Institute of Oceanography, Dartmouth, Canada

Graduate Student

Christopher Meinen, Univ. of Rhode Island, Kingston, RIPhD received: Spring 1998

This project was supported by the National Oceanic and Atmospheric Administration and the Office of Naval Research.

In a collaborative experiment between the University of Rhode Island and the Bedford Institute of Oceanography, a line of inverted echo sounders, bottom pressure sensors, and current meter moorings were deployed across the North Atlantic Current along WOCE line ACM6. The purpose was to determine the structure and transport of the North Atlantic Current at a location where historical hydrographic studies indicated that a short line of moored instruments could consistently capture all of the North Atlantic Current transport. The moorings were in place from August 1993 through February 1995.

Eight current meter moorings with up to 7 levels instrumented (400, 700, 1500, 2500, 3500, 4000~m, and at 100~m above the bottom) were deployed to directly measure the current within all the major water mass components at the upper, intermediate, deep, and near-bottom levels. The vertical spacing was chosen to define the NAC and deep western boundary current (DWBC) flow, and to provide the data for full-water-column integrations of transport. The lateral spacing of the moorings was chosen to resolve the dominant lateral scales and features of the NAC and western boundary currents at intermediate and deep levels along the sloping topography. The mooring spacing at offshore sites was 60~km, decreasing to about 30~km at the onshore sites.

Six inverted echo sounders equipped with pressure gauges (PIES) were deployed along the same transect. Three of the six PIES sites were located at the same sites as the current moorings and two were at midpoints. The sixth PIES site extended the transect beyond the current meter moorings. Since baroclinic velocity is determined from horizontal gradients of dynamic height measured by the IESs, the calculated velocities apply to the half-way points between the PIESs. The four recovered PIESs provided full-water-column profiles of temperature and relative velocity daily over the 19-month time period. Absolute velocities were obtained by combining these relative velocity profiles with absolute bottom velocities determined from the bottom pressure and deep current measurements.

Relevant Publications

  • Hendry, R. M., D. R. Watts, and C. S. Meinen. Newfoundland Basin sea-level variability from TOPEX/POSEIDON altimetry and inverted echo sounder – bottom pressure measurements. Can. J. Remote Sensing, 28(4):544–555, 2002. (doi:10.5589/m02-057)
  • Meinen, C. S., and D. R. Watts. Vertical structure and transport on a transect across the North Atlantic Current near 42N: Timeseries and mean. J. Geophys. Res., 105:21,869–21,892, 2000. (doi:10.1029/2000JC900097)
  • Meinen, C. S., D. R. Watts, and R. A. Clarke. Absolutely referenced geostrophic velocity and transport on a section across the North Atlantic Current. Deep-Sea Res. I, 47:309–322, 2000. (doi:10.1016/S0967-0637(99)00061-8)
  • Meinen, C. S. Transport of the North Atlantic Current. PhD thesis, Graduate School of Oceanography, Univ. Rhode Island, 1998. 197 pp. (PDF)
  • Meinen, C. S. Structure of the North Atlantic Current in stream-coordinates and the circulation in the Newfoundland Basin. Deep-Sea Res. I, 48:1553–1580, 2001. (doi:10.1016/S0967-0637(00)00103-5)
  • Tracey, K. L., C. S. Meinen, and D. R. Watts. North Atlantic Current inverted echo sounder data report for August 1993- July 1995. GSO Technical Report 96-7, University of Rhode Island, 1996. (PDF)

Presentations

WOCE Conference Halifax, Canada, May 24-29, 1998