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Aspects of the large-scale ocean circulation are investigated by combining observations and numerical models (data assimilation). Primary interests concern the determination and understanding of the ocean's time-evolving state. Others include exploration and assessment of assimilation methods, accuracies of estimates (validation), information content of observations, and completeness of model physics.
The primary observations presently analyzed are altimetry data from TOPEX/POSEIDON. Approximations of the Kalman filter and smoother are explored (steady-state, state reduction, linearization), and used to assimilate altimetry data into a hierarchy of models (e.g., spectral equatorial wave model, shallow water model, primitive equation model). One of our present efforts is an assimilation of TOPEX/POSEIDON data with a global model based on the GFDL Modular Ocean Model. A coarse resolution is employed (2° longitudinal, 1° latitudinal, 12 vertical levels) to study the large-scale variability of the global ocean. Preliminary results demonstrate improvements in the model's circulation (velocity) and hydrographic structure (temperature) as a result of the altimetric assimilation. The model-data synthesis is analyzed to determine the dynamic nature of the changes in circulation underlying the observed sea level fluctuations (wind-driven, diabatically-driven, barotropic vs baroclinic changes, etc).
Future directions include incorporation of other measurements to further constrain and improve the model estimate (e.g., hydrography, current meter, floats, acoustic tomography). Improvements in model physics will also be explored and implemented such as mixed layer dynamics and eddy transport.
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