• Book, J., 1998: Kuroshio variations off southwest Japan. M.S. thesis, Graduate School of Oceanography, University of Rhode Island, 92 pp.

    • Search Google Scholar
    • Export Citation
  • Botnikov, V. N., 1963: Geographical position of the Antarctic convergence zone in the Pacific Ocean. Sov. Antarct. Inf. Bull, 4 , 324327.

    • Search Google Scholar
    • Export Citation
  • Carnes, M. R., , W. J. Teague, , and J. L. Mitchell, 1994: Inference of subsurface thermohaline structure from fields measurable by satellite. J. Atmos. Oceanic Technol, 11 , 551566.

    • Search Google Scholar
    • Export Citation
  • Del Grosso, V. A., 1974: New equation for the speed of sound in natural water (with comparison to other equations). J. Acoust. Soc. Amer, 56 , 10841091.

    • Search Google Scholar
    • Export Citation
  • Fofonoff, N. P., 1962: Dynamics of ocean currents. The SeaIdeas and Observations on Progress in the Study of the Seas. Vol. 1: Physical Oceanography, M. N. Hill, Ed., Wiley-Interscience, 323–395.

    • Search Google Scholar
    • Export Citation
  • Fukumori, I., , and C. Wunsch, 1991: Efficient representation of the North Atlantic hydrographic and chemical distributions. Progress in Oceanography, Vol. 27, Pergamon, 111–195.

    • Search Google Scholar
    • Export Citation
  • He, Y., , D. R. Watts, , and K. L. Tracey, 1998: Determining geostrophic velocity shear profiles with IESs. J. Geophys. Res, 103 , 56075622.

    • Search Google Scholar
    • Export Citation
  • Hogg, N. G., 1991: Mooring motion corrections revisited. J. Atmos. Oceanic Technol, 8 , 289295.

  • Killworth, P. D., 1992: An equivalent-barotropic mode in the fine resolution antarctic model. J. Phys. Oceanogr, 22 , 13791387.

  • Lagerloef, G., 1994: An alternate method for estimating dynamic height from XBT profiles using empirical modes. J. Phys. Oceanogr, 24 , 205213.

    • Search Google Scholar
    • Export Citation
  • Luther, D. S., , D. R. Watts, , A. D. Chave, , J. G. Richman, , S. R. Rintoul, , J. A. Church, , and J. H. Filloux, 1998: Sub-Antarctic Flux and Dynamics Experiment (SAFDE): Overview with some descriptive results. Abstracts, WOCE Conf. on Ocean Circulation and Climate, Halifax, NS, Canada, p. 67.

    • Search Google Scholar
    • Export Citation
  • Meinen, C. S., , and D. R. Watts, 1997: Further evidence that the sound speed algorithm of Del Grosso is more accurate than that of Chen and Millero. J. Acoust. Soc. Amer, 102 , 20582062.

    • Search Google Scholar
    • Export Citation
  • Meinen, C. S., , and D. R. Watts, 2000: Vertical structure and transport on a transect across the North Atlantic Current near 42°N. J. Geophys. Res, 105 , 21 86921 891.

    • Search Google Scholar
    • Export Citation
  • Morse, P. M., , and H. Feshbach, 1953: Methods of Theoretical Physics. Vol. 2, McGraw-Hill, 1978 pp.

  • Olbers, D., , V. Gouretski, , G. Seiß, , and J. Schröter, 1992: Hydrographic Atlas of the Southern Ocean. Alfred Wegener Institute, 17 pp. and 82 plates.

    • Search Google Scholar
    • Export Citation
  • Pickart, R. S., , and D. R. Watts, 1990: Using the inverted echo sounder to measure vertical profiles of Gulf Stream temperature and geostrophic velocity. J. Atmos. Oceanic Technol, 7 , 146156.

    • Search Google Scholar
    • Export Citation
  • Richman, J. G., , C. Wunsch, , and N. G. Hogg, 1977: Space and time scales and mesoscale motion in the sea. Rev. Geophys. Space Phys, 15 , 385420.

    • Search Google Scholar
    • Export Citation
  • Rintoul, S. R., , and J. Bullister, 1999: A late winter hydrographic section between Tasmania and Antarctica. Deep-Sea Res, 46 , 14171454.

    • Search Google Scholar
    • Export Citation
  • Rintoul, S. R., , J-R. Donguy, , and D. Roemmich, 1997: Seasonal evolution of upper ocean thermal structure between Tasmania and Antarctica. Deep-Sea Res, 44 , 11851202.

    • Search Google Scholar
    • Export Citation
  • Rosenberg, M., , R. Eriksen, , and S. Rintoul, 1995a: Aurora Australis Marine Science Cruise AU9309/AU9391—Oceanographic field measurements and analysis. Antarctic Cooperative Research Centre Res. Rep. 2, 103 pp.

    • Search Google Scholar
    • Export Citation
  • Rosenberg, M., , R. Eriksen, , S. Bell, , N. Bindoff, , and S. Rintoul, 1995b: Aurora Australis Marine Science Cruise AU9407−Oceanographic field measurements and analysis. Antarctic Cooperative Research Centre Res. Rep. 6, 97 pp.

    • Search Google Scholar
    • Export Citation
  • Rosenberg, M., , R. Eriksen, , S. Bell, , and S. Rintoul, 1996: Aurora Australis Marine Science Cruise AU9404−Oceanographic field measurements and analysis. Antarctic Cooperative Research Centre Res. Rep. 8, 53 pp.

    • Search Google Scholar
    • Export Citation
  • Rosenberg, M., , S. Bray, , N. Bindoff, , S. Rintoul, , N. Johnston, , S. Bell, , and P. Towler, 1997: Aurora Australis Marine Science Cruises AU9501, AU9604, and AU9601−Oceanographic field measurements and analysis, Inter-cruise comparisons and data quality notes. Antarctic Cooperative Research Centre Res. Rep. No. 12, 150 pp.

    • Search Google Scholar
    • Export Citation
  • Sun, C., , and D. R. Watts, 2001: A circumpolar gravest empirical mode for the southern ocean hydrography. J. Geophys. Res, 106 , 28332855.

    • Search Google Scholar
    • Export Citation
  • Tracey, K. L., , S. D. Howden, , and D. R. Watts, 1997: IES calibration and mapping procedures. J. Atmos. Oceanic Technol, 14 , 14831493.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 232 232 50
PDF Downloads 61 61 9

A Two-Dimensional Gravest Empirical Mode Determined from Hydrographic Observations in the Subantarctic Front

View More View Less
  • 1 Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island
  • | 2 Antarctic CRC and CSIRO Marine Research, Hobart, Australia
© Get Permissions Rent on DeepDyve
Restricted access

Abstract

South of Australia, where the baroclinicity in the Subantarctic Front extends almost to the seafloor, the geopotential height of the sea surface (ϕ) and the vertical acoustic travel time (τ) exhibit a tight empirical relationship to each other and to the entire vertical structure of temperature T(p), salinity S(p), and specific volume anomaly δ(p). Measurements of τ provide proxy estimates of the profiles TG(τ, p), SG(τ, p), and δG(τ, p), based on a two-dimensional “gravest empirical mode” (GEM) representation of the vertical structure fitted to 212 hydrographic stations. A seasonal model was fitted in the near-surface layers using additional historical data. At each depth in the range 150–3000 dbar, more than 96% of the variance in both the T and δ fields is captured by the GEM representation.

During the Subantarctic Flux and Dynamics Experiment (Mar 1995–Mar 1997), inverted echo sounders (IES) and current meters were moored in a 2D array along the WOCE SR3 transect south of Australia. At each IES site, proxy-estimated T(p) time series were compared with independent moored temperature records, confirming agreement within 0.29°, 0.26°, 0.10°, and 0.04°C rms differences at depths 300, 600, 1000, and 2000 dbar. Between laterally separated IES sites, geostrophic velocity profiles estimated from horizontal gradients in ϕ(p) agree with moored current records within 0.07, 0.05, and 0.03 m s−1 at 300, 600, and 1000 dbar relative to 2000 dbar. A simple argument based on conservation of potential vorticity is suggested to account for GEM dominance of the spatiotemporal variability.

Corresponding author address: Prof. D. Randolph Watts, Graduate School of Oceanography, University of Rhode Island, 215 South Ferry Road, Narragansett, RI 02882-1197. Email: rwatts@gso.uri.edu

Abstract

South of Australia, where the baroclinicity in the Subantarctic Front extends almost to the seafloor, the geopotential height of the sea surface (ϕ) and the vertical acoustic travel time (τ) exhibit a tight empirical relationship to each other and to the entire vertical structure of temperature T(p), salinity S(p), and specific volume anomaly δ(p). Measurements of τ provide proxy estimates of the profiles TG(τ, p), SG(τ, p), and δG(τ, p), based on a two-dimensional “gravest empirical mode” (GEM) representation of the vertical structure fitted to 212 hydrographic stations. A seasonal model was fitted in the near-surface layers using additional historical data. At each depth in the range 150–3000 dbar, more than 96% of the variance in both the T and δ fields is captured by the GEM representation.

During the Subantarctic Flux and Dynamics Experiment (Mar 1995–Mar 1997), inverted echo sounders (IES) and current meters were moored in a 2D array along the WOCE SR3 transect south of Australia. At each IES site, proxy-estimated T(p) time series were compared with independent moored temperature records, confirming agreement within 0.29°, 0.26°, 0.10°, and 0.04°C rms differences at depths 300, 600, 1000, and 2000 dbar. Between laterally separated IES sites, geostrophic velocity profiles estimated from horizontal gradients in ϕ(p) agree with moored current records within 0.07, 0.05, and 0.03 m s−1 at 300, 600, and 1000 dbar relative to 2000 dbar. A simple argument based on conservation of potential vorticity is suggested to account for GEM dominance of the spatiotemporal variability.

Corresponding author address: Prof. D. Randolph Watts, Graduate School of Oceanography, University of Rhode Island, 215 South Ferry Road, Narragansett, RI 02882-1197. Email: rwatts@gso.uri.edu

Save