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Ocean data assimilation efforts of the Global Modeling and Assimilation Office (GMAO) at NASA/Goddard Space Flight Center are directed towards seasonal-to-interannual climate prediction using coupled ocean-atmosphere-land surface general circulation models. The primary ocean data assimilation goal is to provide the best possible ocean initialisation for climate prediction. GMAO activities and progress in ocean data assimilation are documented at http://gmao.gsfc.nasa.gov/research/oceanassim/.

1. Input Data Forcing data: Near real time SSMI and Scatterometer-based surface wind analyses; Surface heat flux from NCEP CDAS with relaxation to Reynolds SST, GPCP precipitation.

In situ data: ARGO data from GODAE server in Monterey; mooring data from PMEL; other profile data from NCEP; synthetic salinity profiles from Levitus 94 climatology.

SST: Reynolds SST product.

2. Data Serving (if Relevant)
N/A

3. Model
GMAO uses the Poseidon V4 quasi-isopycnal ocean model. The model is run quasi-globally from Antarctica to 70&degN with a buffer zone at the northern boundary. The model resolution is 1/3° meridionally and 5/8° zonally with 27 vertical coordinate surfaces.

4. Assimilation Method
The analyses distributed on the USGODAE LAS site use a Univariate Optimal Interpolation (UOI) to assimilate temperature profiles. A separate salinity analysis is generated using Argo salinity profiles and synthetic salinity profiles derived for each XBT temperature profile from Levitus T-S climatology. The forecast temperature and salinity error covariances are Gaussian. In the equatorial region, the decorrelation scales for temperature are 20° in the zonal direction and 4° in the meridional direction. The vertical decorrelation scale is 100 meters. For salinity assimilation, the decorrelation scales are 8° in the zonal direction and 3° in the meridional direction. The vertical decorrelation scale is 40 meters. Away from the equator the horizontal scales become more isotropic. The standard deviation of observational error for temperature is taken to be 0.5&degC for all instrument types so as to include representation error. The standard deviation of the forecast temperature error is 0.7&degC. For salinity, the standard deviation of observational error from Argo profiles is taken to be 10% of the forecast error, and the synthetic profiles are assumed to have twice the standard deviation of the forecast error. Salinity is not updated within the mixed layer.

5. Assimilitation products and dissemination
GMAO ocean analyses are openly available from a link on the USGODAE web site(http://usgodae3.fnmoc.navy.mil/projects.html): http://ferret.pmel.noaa.gov/GODAE/servlets/dataset. Data products include monthly mean surface forcing, temperature and salinity profiles and zonal and meridional current profiles.

6. Systems
In addition to our existing quasi-global OI system, we have multi-variate assimilation systems using both static and evolutionary statistics through ensemble methods. The Ensemble Kalman Filter (EnKF) system is being used to assimilate altimeter data in addition to the conventional in situ data streams. During 2006, we will update the analysis model to Poseidon V5.

7. Links with GODAE pilot projects (Argo, GHRSST)
Argo data from the USGODAE site are routinely included in the analysis, after additional QC. We are currently undertaking a study to evaluate the impact of the Argo data on our analyses.

8. Internal metrics and intercomparison plans
Internal metrics include comparison against assimilated and independent data in the tropical oceans and impact of the analysis on forecast skill. Other metrics are those designed for comparisons as part of the Ocean Data Assimilation for Seasonal-to-Interannual prediction (ODASI) Consortium. Experiments have been undertaken to evaluate different assimilation systems using the GODAE diagnostics metrics. Using the same input data streams and quality-controlled observations as other participants, a common set of output data has been generated for evaluation. Details are documented on the ODASI Consortium website.

9. Users and external metrics
GMAO products are focused towards its S-I forecasts. The external metric is 3, 6, 9 and 12-month forecasts of Ni�o-3 SST and Equatorial Pacific thermocline anomalies.

10. Reanalysis activities (if any)
Existing analyses focus on the period from 1993 to the present. During 2006-2007, GMAO plans to conduct a reanalysis of the period from 1970 to present using an updated model, Poseidon V5.

11. Computing resources
Computer resources are provided through the NASA Center for Computational Sciences at NASA/Goddard Space Flight Center.

12. Consolidation phase and transition to operational systems (activities)
The ocean assimilation system included on the USGODAE LAS site has now been included in the GMAO experimental forecast production. We are in the process of testing MOM4 so that developments may also be tested for the NCEP operational system and included in multi-model forecast experiments.