The Global Ocean Circulation Estimated from 
TOPEX/POSEIDON Altimetry and the 
MIT General Circulation Model

In a first application we demonstrated the beginning of a global ocean circulation estimation system. A preliminary estimates was made of the global circulation as it emerges from constraining the MIT general circulation model by TOPEX/POSEIDON altimeter data from the year 1993. The model is forced to consistency with those data by using the models adjoint to modify the initial temperature and salinity fields over the full water column and to adjust the meteorological forcing fields for momentum, heat and fresh water. Results differ from either the model or the data alone, and describe a time-evolving state which --- based on the prescribed error statistics --- appear to be consistent with: (1) the absolute T/P sea surface height relative to the EGM96 geoid model, (2) the time dependent T/P sea surface height component, (3) 10-day averages of NCEP surface fluxes of momentum, heat and fresh water, and (4) the annual mean theta, S climatology. From the present preliminary solution no obstacles are foreseen to obtain a more definitive solutions using all available observations, improved error statistics and improved model configurations.

A full report on the preliminary global state estimation is given at http://puddle.mit.edu/~detlef/OSE/report_0/index.html .

Computations now underway are directed at greatly extending and improving the preliminary computation. Improvements include an increased model resolution to 1, an extended estimation period to 6 years (1992 through 1997), as well as more acurate representations of straits and sills in the topography. Equally important, a complete mixed layer model (Large et al., 1994) and an eddy parameterization (Gent and McWilliams, 1990) have been incorporated into the adjoint model. Moreover, a full (non-diagonal) geoid error covariance matrix is being used as well as other improvements in the remaining weights.
Click here for a present status report of the ongoing global ocean state estimation over a 6 year period covering 1992 through 1997.

The set of computations now underway is still regarded as preliminary. The model resolution will eventually be greatly increased and as much as possible of the entire WOCE data set will be used. The combination of the OGCM with data, each appropriately weighted by its uncertainty estimates, should provide a useful basic description of the ocean circulation and its variability. Among many possible applications, one expects the production of much better estimates of property flux divergences, and the study of oceanic biogeochemical cycles which are dependent upon the circulation.
 

An animation of 6 years of model SSH anomaly fields obtained from 30th iteration can be viewed here. Note that the title shows day numbers.
An animation of 6 years of estimated changes in NCEP net sea surface heat fluxes which are required to bring the model into consistency with the data.
An animation of 6 years of estimated changes in NCEP net sea surface fresh water fluxes which are required to bring the model into consistency with the data.