• Acero-Schertzer, C. E., D. V. Hansen, and M. S. Swenson, 1997: Evaluation and diagnosis of surface currents in the National Centers for Environmental Prediction’s ocean analyses. J. Geophys. Res.,102, 21 037–21 048.

    • Crossref
    • Export Citation
  • Anderson, D. L. T., J. Sheinbaum, and K. Haines, 1996: Data assimilation in ocean models. Rev. Prog. Phys.,59, 1209–1266.

    • Crossref
    • Export Citation
  • Cane, M. A., and E. S. Sarachik, 1979: Forced baroclinic ocean motion. III. The linear equatorial basin case. J. Mar. Res.,37, 355–398.

  • Carton, J. A., B. S. Giese, X. Cao, and L. Miller, 1996: Impact of altimeter, thermistor, and expendable bathythermograph data on retrospective analyses of the tropical Pacific Ocean. J. Geophys. Res.,101, 14 147–14 159.

    • Crossref
    • Export Citation
  • Chen, D., L. M. Rothstein, and A. J. Busalacchi, 1994: A hybrid vertical mixing scheme and its application to tropical ocean models. J. Phys. Oceanogr.,24, 2156–2179.

    • Crossref
    • Export Citation
  • Delcroix, T., G. Eldin, M. McPhaden, and A. Morliere, 1993: Effects of westerly wind bursts upon the western equatorial Pacific Ocean, February–April 1991. J. Geophys. Res.,98, 16 379–16 385.

    • Crossref
    • Export Citation
  • Eldin, G., M. Rodier, and M.-H. Radenac, 1997: Physical and nutrient variability in the upper equatorial Pacific with westerly wind forcing and wave activity in October 1994. Deep-Sea Res.,44, 1783–1800.

    • Crossref
    • Export Citation
  • Enfield, D. B., and J. E. Harris, 1995: A comparative study of tropical Pacific sea surface height variability: Tide gauges versus the National Meteorological Center data-assimilating ocean general circulation model, 1982–1992. J. Geophys. Res.,100, 8661–8675.

    • Crossref
    • Export Citation
  • Fukumori, I., 1995: Assimilation of TOPEX sea level measurements with a reduced-gravity, shallow water model of the tropical Pacific Ocean. J. Geophys. Res.,100, 25 027–25 039.

    • Crossref
    • Export Citation
  • Goddard, L., and N. E. Graham, 1997: El Niño in the 1990s. J. Geophys. Res.,102, 10 423–10 436.

  • Gouriou, Y., and J. Toole, 1993: Mean circulation of the upper layers of the western equatorial Pacific Ocean. J. Geophys. Res.,98, 22 495–22 520.

    • Crossref
    • Export Citation
  • Halpern, D., Y. Chao, C.-C. Ma, and C. R. Mechoso, 1995: Comparison of tropical Pacific temperature and current simulations with two vertical mixing schemes embedded in an ocean general circulation model and reference to observations. J. Geophys. Res.,100, 2515–2522.

    • Crossref
    • Export Citation
  • Hanawa, K., P. Rual, R. Bailey, A. Sy, and M. Szabados, 1995: A new depth-time equation for Sippican or TSK T-7, T-6 and T-4 expendable bathythermographs (XBT). Deep-Sea Res.,42, 1423–1451.

  • Hao, Z., and M. Ghil, 1994: Data assimilation in a simple tropical ocean model with wind stress errors. J. Phys. Oceanogr.,24, 2111–2128.

    • Crossref
    • Export Citation
  • Ji, M., and T. M. Smith, 1995: Ocean model response to temperature data assimilation and varying surface wind stress: Intercomparisons and implications for climate forecast. Mon. Wea. Rev.,123, 1811–1821.

    • Crossref
    • Export Citation
  • ——, A. Leetmaa, and J. Derber, 1995: An ocean analysis system for seasonal to interannual climate studies. Mon. Wea. Rev.,123, 460–481.

    • Crossref
    • Export Citation
  • Leetmaa, A., and M. Ji, 1989: Operational hindcasting of the tropical Pacific. Dyn. Atmos. Oceans,13, 465–490.

    • Crossref
    • Export Citation
  • ——, and ——, 1996: Ocean data assimilation as a component of a climate forecast system. Modern Approaches to Data Assimilation in Ocean Modeling, P. Malanotte-Rizzoli, Ed., Elsevier, 271–293.

    • Crossref
    • Export Citation
  • Malanotte-Rizzoli, P., and E. Tziperman, 1996: The oceanographic data assimilation problem: Overview, motivation and purposes. Modern Approaches to Data Assimilation in Ocean Modeling, P. Malanotte-Rizzoli, Ed., Elsevier, 3–17.

    • Crossref
    • Export Citation
  • McPhaden, M. J., 1995: The Tropical Atmosphere–Ocean array is completed. Bull. Amer. Meteor. Soc.,76, 739–741.

    • Crossref
    • Export Citation
  • Mellor, G. L., and T. Yamada, 1982: Development of a turbulence closure model for geophysical fluid problems. Rev. Geophys.,20, 851–875.

    • Crossref
    • Export Citation
  • Murtugudde, R., and A. J. Busalacchi, 1998: Salinity effects in a tropical ocean model. J. Geophys. Res.,103, 3283–3300.

    • Crossref
    • Export Citation
  • Pacanowski, R. C., and S. G. H. Philander, 1981: Parameterization of vertical mixing in numerical models of tropical oceans. J. Phys. Oceanogr.,11, 1443–1451.

    • Crossref
    • Export Citation
  • Philander, S. G. H., W. Hurlin, and A. D. Seigel, 1987: A model of the seasonal cycle in the tropical Pacific Ocean. J. Phys. Oceanogr.,17, 1986–2002.

    • Crossref
    • Export Citation
  • ——, and Coauthors, 1985: Long waves in the equatorial Pacific Ocean. Eos, Trans. Amer. Geophys. Union,66, 154.

    • Crossref
    • Export Citation
  • Plimpton, P. E., H. P. Freitag, and M. J. McPhaden, 1997: ADCP velocity errors from pelagic fish schooling around equatorial moorings. J. Atmos. Oceanic Technol.,14, 1212–1223.

    • Crossref
    • Export Citation
  • Reynolds, R. W., M. Ji, and A. Leetmaa, 1998: Use of salinity to improve ocean modeling. Phys. Chem. Earth,23, 545–555.

    • Crossref
    • Export Citation
  • Rosati, A., and K. Miyakoda, 1988: A general circulation model for upper ocean simulation. J. Phys. Oceanogr.,18, 1601–1626.

    • Crossref
    • Export Citation
  • Schopf, P. S., and A. Loughe, 1995: A reduced-gravity isopycnal ocean model: Hindcasts of El Niño. Mon. Wea. Rev.,123, 2839–2863.

    • Crossref
    • Export Citation
  • Weisberg, R. H., and C. Wang, 1997: Slow variability in the equatorial west-central Pacific in relation to ENSO. J. Climate,10, 1998–2017.

  • Wijesekera, H. W., and M. C. Gregg, 1996: Surface layer response to weak winds, westerly bursts, and rain squalls in the western Pacific warm pool. J. Geophys. Res.,101, 977–997.

    • Crossref
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 100 100 2
PDF Downloads 7 7 3

Influence of Assimilation of Subsurface Temperature Measurements on Simulations of Equatorial Undercurrent and South Equatorial Current along the Pacific Equator

View More View Less
  • 1 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
  • | 2 National Centers for Environmental Prediction, National Oceanic and Atmospheric Administration, Camp Springs, Maryland
© Get Permissions Rent on DeepDyve
Restricted access

Abstract

Equatorial Pacific current and temperature fields were simulated with and without assimilation of subsurface temperature measurements for April 1992–March 1995 and compared with moored buoy and research vessel current measurements. Data assimilation intensified the mean east–west slope of the thermocline along the equator in the eastern Pacific, shifted eastward the longitude of the mean Equatorial Undercurrent (EUC) maximum speed 800 km to 125°W, and produced a 25% stronger mean EUC core speed in the eastern Pacific. In the eastern Pacific the mean EUC core speed simulated with data assimilation was slightly more representative of observations compared to that computed without data assimilated; in the western Pacific the data assimilation had no impact on mean EUC simulations.

Data assimilation intensified the north–south slope of the thermocline south of the equator in the western Pacific to produce a thicker and more intense westward-flowing South Equatorial Current (SEC) in the western Pacific. In the western Pacific the mean SEC transport per unit width simulated with data assimilation was more representative of observations compared to that computed without data assimilation. However, large differences remained between the observed SEC transport per unit width and that simulated with data assimilation. In the eastern Pacific, the data assimilation had no impact on mean SEC simulations.

The temporal variability of monthly mean EUC core speeds and SEC transports per unit width were increased significantly by data assimilation. It also increased the representativeness of monthly mean SEC transports per unit width to the observations. However, the data representativeness of monthly mean EUC core speeds was decreased. Results could be explained by the coupling between zonal gradient of temperature and EUC and between meridional gradient of temperature and SEC. Longitudinal variations along the Pacific equator of the impact of data assimilation on the EUC and SEC precludes the choice of a single site to evaluate the effectiveness of data assimilation schemes.

Corresponding author address: Dr. David Halpern, Jet Propulsion Laboratory, MS 300-323, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099.

Email: halpern@pacific.jpl.nasa.gov

Abstract

Equatorial Pacific current and temperature fields were simulated with and without assimilation of subsurface temperature measurements for April 1992–March 1995 and compared with moored buoy and research vessel current measurements. Data assimilation intensified the mean east–west slope of the thermocline along the equator in the eastern Pacific, shifted eastward the longitude of the mean Equatorial Undercurrent (EUC) maximum speed 800 km to 125°W, and produced a 25% stronger mean EUC core speed in the eastern Pacific. In the eastern Pacific the mean EUC core speed simulated with data assimilation was slightly more representative of observations compared to that computed without data assimilated; in the western Pacific the data assimilation had no impact on mean EUC simulations.

Data assimilation intensified the north–south slope of the thermocline south of the equator in the western Pacific to produce a thicker and more intense westward-flowing South Equatorial Current (SEC) in the western Pacific. In the western Pacific the mean SEC transport per unit width simulated with data assimilation was more representative of observations compared to that computed without data assimilation. However, large differences remained between the observed SEC transport per unit width and that simulated with data assimilation. In the eastern Pacific, the data assimilation had no impact on mean SEC simulations.

The temporal variability of monthly mean EUC core speeds and SEC transports per unit width were increased significantly by data assimilation. It also increased the representativeness of monthly mean SEC transports per unit width to the observations. However, the data representativeness of monthly mean EUC core speeds was decreased. Results could be explained by the coupling between zonal gradient of temperature and EUC and between meridional gradient of temperature and SEC. Longitudinal variations along the Pacific equator of the impact of data assimilation on the EUC and SEC precludes the choice of a single site to evaluate the effectiveness of data assimilation schemes.

Corresponding author address: Dr. David Halpern, Jet Propulsion Laboratory, MS 300-323, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099.

Email: halpern@pacific.jpl.nasa.gov

Save