Variational assimilation of ocean tomographic data: Twin experiments in a quasi‐geostrophic model

The possibility of using tomography data as a constraint in variational data assimilation is explored by performing twin experiments. Realistic travel-time data are generated in a quasi-geostrophic model applied to the western Mediterranean Sea. After checking the robustness of the method with this dataset, a sensitivity study analyses the propagation of information by the model, and tests the effect of different parameters such as the starting point of the optimization or the length of the assimilation period. It appears that the variational method is well adapted to the nature of tomographic data that provide at the same time high time resolution and space integrals. The results clearly show the ability of this dataset to recover the temporal evolution of heat content in each layer and improve various components of the circulation described by the model. Tomography must then be considered as an important source of information that may contribute with altimetry or local in situ measurement to the description of the ocean state and its evolution. Copyright © 2002 Royal Meteorological Society.

[1]  Monique Tanguay,et al.  Four‐dimensional data assimilation with a wide range of scales , 1995 .

[2]  B. Cornuelle,et al.  Ocean acoustic tomography , 1988, Signal Recovery and Synthesis.

[3]  F. Veerse,et al.  Multiple‐truncation incremental approach for four‐dimensional variational data assimilation , 1998 .

[4]  W. Thacker,et al.  Fitting dynamics to data , 1988 .

[5]  F. Schott,et al.  A four‐dimensional analysis of the thermal structure in the Gulf of Lion , 1997 .

[6]  Bruno Luong,et al.  A variational method for the resolution of a data assimilation problem in oceanography , 1998 .

[7]  C. Millot.  Circulation in the Western Mediterranean Sea , 1999 .

[8]  J. Sheinbaum.  Variational assimilation of simulated acoustic tomography data and point observations: A comparative study , 1995 .

[9]  Arthur B. Baggeroer,et al.  The Transarctic Acoustic Propagation Experiment and climate monitoring in the Arctic , 1999 .

[10]  B. Dushaw.  Inversion of multimegameter-range acoustic data for ocean temperature , 1999 .

[11]  Fabienne Gaillard,et al.  Evaluating the information content of tomographic data: Application to mesoscale observations , 1992 .

[12]  M. Crépon,et al.  A Sensitivity Study of the General Circulation of the Western Mediterranean Sea. Part I: The Response to Density Forcing through the Straits , 1996 .

[13]  B. Dushaw,et al.  Observing the ocean in the 2000s: a strategy for the role of acoustic tomography in ocean climate observation , 2001 .

[14]  Carl Wunsch,et al.  Basin-scale ocean circulation from combined altimetric, tomographic and model data , 1997, Nature.

[15]  William R. Holland,et al.  The Role of Mesoscale Eddies in the General Circulation of the Ocean—Numerical Experiments Using a Wind-Driven Quasi-Geostrophic Model , 1978 .

[16]  D. Mauuary,et al.  Acoustic observations of heat content across the Mediterranean Sea , 1997, Nature.

[17]  Philippe Courtier,et al.  Unified Notation for Data Assimilation : Operational, Sequential and Variational , 1997 .

[18]  F. Schott,et al.  Observation of a deep convection regime with acoustic tomography , 1995 .

[19]  B. Cornuelle,et al.  Three-Dimensional Observations of a Deep Convective Chimney in the Greenland Sea during Winter 1988/89 , 1996 .

[20]  F. L. Dimet,et al.  Variational algorithms for analysis and assimilation of meteorological observations: theoretical aspects , 1986 .

[21]  W. R. Holland,et al.  Gyre-Scale Acoustic Tomography: Modeling Simulations , 1985 .

[22]  Carl Wunsch,et al.  Ocean acoustic tomography: a scheme for large scale monitoring , 1979 .