• Bell, M. J., M. J. Martin, and N. K. Nichols, 2004: Assimilation of data into an ocean model with systematic errors near the equator. Quart. J. Roy. Meteor. Soc., 130 , 873893.

    • Search Google Scholar
    • Export Citation
  • Bloom, S. C., L. L. Takacs, A. M. Da Silva, and D. Levina, 1996: Data assimilation using incremental analysis updates. Mon. Wea. Rev., 124 , 12561271.

    • Search Google Scholar
    • Export Citation
  • Burgers, G., M. Alonso Balmaseda, F. C. Vossepoel, G. J. van Oldenborgh, and P. J. van Leeuwen, 2002: Balanced ocean-data assimilation near the equator. J. Phys. Oceanogr., 32 , 25092519.

    • Search Google Scholar
    • Export Citation
  • Cooper, N. S., 1988: The effect of salinity in tropical ocean models. J. Phys. Oceanogr., 18 , 697707.

  • Derber, J., and A. Rosati, 1989: A global oceanic data assimilation system. J. Phys. Oceanogr., 19 , 13331347.

  • Derber, J., and F. Bouttier, 1999: A reformulation of the background error covariance in the ECMWF global data assimilation system. Tellus, 51A , 195221.

    • Search Google Scholar
    • Export Citation
  • Gilbert, J-C., and C. Lemaréchal, 1989: Some numerical experiments with variable storage quasi-Newton algorithms. Math. Programm., 45 , 407435.

    • Search Google Scholar
    • Export Citation
  • Huffman, G. J., and Coauthors, 1997: The Global Precipitation Climatology Project (GPCP) combined precipitation dataset. Bull. Amer. Meteor. Soc., 78 , 520.

    • Search Google Scholar
    • Export Citation
  • Ide, K., P. Courtier, M. Ghil, and A. C. Lorenc, 1997: Unified notation for data assimilation: Operational, sequential and variational. J. Meteor. Soc. Japan, 75 , 181189.

    • Search Google Scholar
    • Export Citation
  • Ji, M., R. W. Reynolds, and D. Behringer, 2000: Use of TOPEX/Poseidon sea level data for ocean analysis and ENSO prediction: Some early results. J. Climate, 13 , 216231.

    • Search Google Scholar
    • Export Citation
  • Johnson, G., B. M. Sloyan, W. S. Kessler, and K. E. McTaggart, 2002: Direct measurements of upper ocean currents and water properties across the tropical Pacific during the 1990s. Progress in Oceanography, Vol. 52, Pergamon, 31–61.

    • Search Google Scholar
    • Export Citation
  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77 , 437471.

  • Levitus, S., R. Burgett, and T. P. Boyer, 1994: Salinity. Vol. 3, World Ocean Atlas 1994, NOAA Atlas NESDIS 3, 99 pp.

  • Lorenc, A. C., 2003: Modelling of error covariances by four-dimensional variational data assimilation. Quart. J. Roy. Meteor. Soc., 129 , 31673182.

    • Search Google Scholar
    • Export Citation
  • Lukas, R., and E. Lindström, 1991: The mixed layer of the western equatorial Pacific Ocean. J. Geophys. Res., 96 , 33433357.

  • Madec, G., P. Delecluse, M. Imbard, and C. Levy, 1998: OPA 8.1 Ocean General Circulation Model reference manual. LODYC/IPSL Tech. Note 11, Paris, France, 91 pp.

  • Maes, C., and D. Behringer, 2000: Using satellite-derived sea level and temperature profiles for determining the salinity variability: A new approach. J. Geophys. Res., 105 , 85378548.

    • Search Google Scholar
    • Export Citation
  • Maes, C., D. Behringer, R. W. Reynolds, and M. Ji, 2000: Retrospective analysis of the salinity variability in the western tropical Pacific Ocean using an indirect minimization approach. J. Atmos. Oceanic Technol., 17 , 512524.

    • Search Google Scholar
    • Export Citation
  • McPhaden, M. J., and Coauthors, 1998: The Tropical Ocean-Global Atmosphere observing system: A decade of progress. J. Geophys. Res., 103 , 1416914240.

    • Search Google Scholar
    • Export Citation
  • Picaut, J., and R. Tournier, 1991: Monitoring the 1979–1985 equatorial Pacific current transports with expendable bathythermograph data. J. Geophys. Res., 96 , 32633277.

    • Search Google Scholar
    • Export Citation
  • Reynolds, R. W., and T. M. Smith, 1994: Improved global sea surface temperature analyses using optimal interpolation. J. Climate, 7 , 929948.

    • Search Google Scholar
    • Export Citation
  • Roemmich, D., M. Morris, W. R. Young, and J. R. Donguy, 1994: Fresh equatorial jets. J. Phys. Oceanogr., 24 , 540558.

  • Roemmich, D., and Coauthors, 2001: Argo: The global array of profiling floats. Observing the Oceans in the 21st Century, C. J. Koblinsky and N. R. Smith, Eds., GODAE Project Office, Bureau of Meteorology, Australia, 248–257.

    • Search Google Scholar
    • Export Citation
  • Tarantola, A., 1987: Inverse Problem Theory: Methods for Data Fitting and Model Parameter Estimation. Elsevier, 613 pp.

  • Troccoli, A., and K. Haines, 1999: Use of temperature–salinity relation in a data assimilation context. J. Atmos. Oceanic Technol., 16 , 20112025.

    • Search Google Scholar
    • Export Citation
  • Troccoli, A., M. Alonso Balmaseda, J. Segschneider, J. Vialard, D. L. T. Anderson, T. Stockdale, K. Haines, and A. D. Fox, 2002: Salinity adjustments in the presence of temperature data assimilation. Mon. Wea. Rev., 130 , 89102.

    • Search Google Scholar
    • Export Citation
  • Vialard, J., and P. Delecluse, 1998a: An OGCM study for the TOGA decade. Part I: Role of the salinity in the physics of the western Pacific fresh pool. J. Phys. Oceanogr., 28 , 10711088.

    • Search Google Scholar
    • Export Citation
  • Vialard, J., and P. Delecluse, 1998b: An OGCM study for the TOGA decade. Part II: Barrier layer formation and variability. J. Phys. Oceanogr., 28 , 10891106.

    • Search Google Scholar
    • Export Citation
  • Vialard, J., C. Menkes, J-P. Boulanger, P. Delecluse, E. Guilyardi, and M. J. McPhaden, 2001: A model study of the oceanic mechanisms affecting the equatorial SST during the 1997–98 El Niño. J. Phys. Oceanogr., 31 , 16491675.

    • Search Google Scholar
    • Export Citation
  • Vialard, J., P. Delecluse, and C. Menkes, 2002: A modeling study of salinity variability and its effects in the tropical Pacific Ocean during the 1993–99 period. J. Geophys. Res., 107 .8005, doi:10.1029/2000JC000758.

    • Search Google Scholar
    • Export Citation
  • Vialard, J., A. T. Weaver, D. L. T. Anderson, and P. Delecluse, 2003: Three- and four-dimensional variational assimilation with a general circulation model of the tropical Pacific Ocean. Part II: Physical validation. Mon. Wea. Rev., 131 , 13791395.

    • Search Google Scholar
    • Export Citation
  • Vossepoel, F. C., and D. W. Behringer, 2000: Impact of sea level assimilation on salinity variability in the western equatorial Pacific. J. Phys. Oceanogr., 30 , 17061721.

    • Search Google Scholar
    • Export Citation
  • Weaver, A. T., and P. Courtier, 2001: Correlation modelling on the sphere using a generalized diffusion equation. Quart. J. Roy. Meteor. Soc., 127 , 18151846.

    • Search Google Scholar
    • Export Citation
  • Weaver, A. T., J. Vialard, and D. L. T. Anderson, 2003: Three- and four-dimensional variational assimilation with a general circulation model of the tropical Pacific Ocean. Part I: Formulation, internal diagnostics, and consistency checks. Mon. Wea. Rev., 131 , 13601378.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 0 0 0
PDF Downloads 0 0 0

Incorporating State-Dependent Temperature–Salinity Constraints in the Background Error Covariance of Variational Ocean Data Assimilation

View More View Less
  • 1 Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique/SUC URA 1875, Toulouse, France
  • | 2 Laboratoire d’Océanographie Dynamique et de Climatologie, CNRS/IRD/UPMC/MNHN, Paris, France
  • | 3 Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique/SUC URA 1875, Toulouse, France
Restricted access

Abstract

Several studies have illustrated how the univariate assimilation of temperature data can have a detrimental effect on the ocean-state variables (salinity, currents, etc.) not directly constrained by the data. In this paper, the authors describe how the salinity adjustment method proposed by Troccoli and Haines can be included as a multivariate temperature–salinity (TS) constraint within a background-error covariance model for variational data assimilation. The method is applied to a three-dimensional variational assimilation (3DVAR) system for a tropical Pacific version of the Océan Parallélisé (OPA) ocean general circulation model. An identical twin experiment is presented first to illustrate how the method is effective in reconstructing a density profile using only temperature observations from that profile. The 3DVAR system is then cycled over the period 1993–98 using in situ temperature data from the Global Temperature and Salinity Pilot Programme. Relative to a univariate (T) 3DVAR, the multivariate (T, S) 3DVAR significantly improves the salinity mean state. A comparison with salinity data that are not assimilated is also presented. The fit to these observations is improved when the TS constraint is applied. The salinity correction leads to a better preservation of the salinity structure and avoids the development of spurious geostrophic currents that were evident in the univariate analysis. The currents at the surface and below the core of the undercurrent are also improved.

Examination of the heat budget highlights how the temperature increment must compensate for a perpetual degradation of the temperature field by abnormally strong advection in the univariate experiment. When the TS constraint is applied, this spurious advection is reduced and the mean temperature increment is decreased. Examination of the salt budget shows that spurious advection is also the main cause of the upper-ocean freshening. When the TS constraint is applied, the salinity structure is improved allowing for a better representation of the advection term and better preservation of the salt content in the upper ocean. The TS constraint does not correct for all problems linked to data assimilation: vertical mixing is still too strong, and the surface salinity state and currents still have substantial errors. Improvements can be expected by including additional constraints in the background error covariances and by assimilating salinity data.

Corresponding author address: Dr. Anthony Weaver, CERFACS, 42 avenue Gaspard Coriolis, 31057 Toulouse Cedex 1, France. Email: weaver@cerfacs.fr

Abstract

Several studies have illustrated how the univariate assimilation of temperature data can have a detrimental effect on the ocean-state variables (salinity, currents, etc.) not directly constrained by the data. In this paper, the authors describe how the salinity adjustment method proposed by Troccoli and Haines can be included as a multivariate temperature–salinity (TS) constraint within a background-error covariance model for variational data assimilation. The method is applied to a three-dimensional variational assimilation (3DVAR) system for a tropical Pacific version of the Océan Parallélisé (OPA) ocean general circulation model. An identical twin experiment is presented first to illustrate how the method is effective in reconstructing a density profile using only temperature observations from that profile. The 3DVAR system is then cycled over the period 1993–98 using in situ temperature data from the Global Temperature and Salinity Pilot Programme. Relative to a univariate (T) 3DVAR, the multivariate (T, S) 3DVAR significantly improves the salinity mean state. A comparison with salinity data that are not assimilated is also presented. The fit to these observations is improved when the TS constraint is applied. The salinity correction leads to a better preservation of the salinity structure and avoids the development of spurious geostrophic currents that were evident in the univariate analysis. The currents at the surface and below the core of the undercurrent are also improved.

Examination of the heat budget highlights how the temperature increment must compensate for a perpetual degradation of the temperature field by abnormally strong advection in the univariate experiment. When the TS constraint is applied, this spurious advection is reduced and the mean temperature increment is decreased. Examination of the salt budget shows that spurious advection is also the main cause of the upper-ocean freshening. When the TS constraint is applied, the salinity structure is improved allowing for a better representation of the advection term and better preservation of the salt content in the upper ocean. The TS constraint does not correct for all problems linked to data assimilation: vertical mixing is still too strong, and the surface salinity state and currents still have substantial errors. Improvements can be expected by including additional constraints in the background error covariances and by assimilating salinity data.

Corresponding author address: Dr. Anthony Weaver, CERFACS, 42 avenue Gaspard Coriolis, 31057 Toulouse Cedex 1, France. Email: weaver@cerfacs.fr

Save