1. Ocean Reanalysis D. Stammer www.clivar.org

2. Ocean synthesis/reanalysis • Continued development of ocean synthesis • products and reanalysis; some now are truly global, including sea ice, multi-decadal; new EU Arctic reanalysis effort just started. • Exploration of use of syntheses for initialization. • Continuation on joint evaluation efforts and improvements. • Reprocessing of input data sets and prior error information. • 8 Community White paper contributions to OceanObs’09. • First coupled assimilation efforts exist; more developments are ongoing (K7; GFDL; KlimaCampus, ….).

3. Ocean synthesis/reanalysis • Annual CLIVAR/GODAE Ocean Synthesis Workshops • Intercomparison of products from multiple groups • Evaluation of product quality and skill • Identification of system strengths and weaknesses • Definition of climate-relevant indices and standards for assessment GSOP participation in WCRP Earth System Initialization for Decadal Predictions Workshop, Nov 2009 – KNMI, Utrecht, The Netherlands. GSOP participation in St. Michaels (MD) Workshop on: Decadal Climate Variability Decadal Climate Predictability and Prediction WGOMD-GSOP Workshop on Decadal Variability, Predictability and Predictions: Understanding the Role of the Ocean, Boulder, Sept. 2010

4. Need for Climate-oriented Ocean Data Synthesis • Improve understanding of climate variability and climate sensitivities. • Improve climate forecasts by merging coupled models with the climate data base (certainly relevant for SSH predictions). • Assimilation of climate observations is needed to improve model skill: • Improve initial conditions • Improve model parameters • Improve forcing functions/bc.

5. Ongoing Ocean Synthesis • Several global ocean data assimilation products are available today that in principle can be used for climate studies.Basin panels were encouraged to enhance their usage. • Underlying assimilation schemes range from simple and computationally efficient (e.g., optimal interpolation) to sophisticated and computationally intensive (e.g., adjoint and Kalman smoother). • We need to evaluate the skill of each of those estimates in simulating the true ocean and for initialisation of predictions (EasyInit).

6. SSH Error Sources: instrumental errors (Trenberth et al.)

7. Improved Heat Content Estimate (Trenberth et al.)

8. Global Heat Content Anomaly (1022 J) Domingues et al. (2008)

9. z-Level Model No Model NCEP ERA40 MOM MIT OPA/NEMO POP HOPE Relax. QSCATGPCP Bias corr. E-P. Relax. Relax. CORE Relax. K-7 GODAS URDG GECCO GFDL SODA Mercator INGV ECMWF DePreSys EN3 4D-Var 3D-Var/OI .25ox.25o 1ox1o DATA 2ox2o

10. Example: The GECCO State Estimate • Part of the ECCO Consortium Effort (see ecco-group.org). • Ocean synthesis, performed over the period 1952 through 2001 on a 1º global grid with 23 layers in the vertical, using the ECCO/MIT adjoint technology (now extended to present globally). • Optimization started from Levitus and NCEP forcing and uses state of the art physics modules (GM, KPP). • The models adjoint (obtained using TAF) is used to bring the model into consistency with most of the available ocean observations over the full period by adjusting control parameters. • So fare control parameters: initial temperature and salinity fields, surface forcing. Now also included: mixing parameters. • Note: the final run is a free forward run.

11. Comparison GECCO - Observations GECCO Model (1992-2001) Topex/Poseidon (1993-2001) (Köhl et al., 2007)

12. Thermosteric Trend Total Trend 1992 – 2001 (cm) Steric Trend Halosteric Trend

13. ECCO-SIO/50y + Ref. GECCO Bryden et al. (2005)

15. N. Atlantic Temp (0-300 m) WCRP enabling initialized predictions Ocean synthesis/reanalysis

16. Global Synthesis and Observations PanelIntercomparison of the Indonesian Throughflow (ITF) Transport Estimated by Ocean Data Assimilation (ODA) Products (Joint GSOP-IOP activity) Five-year low-pass ITF transport anomaly (color curves) and their ensemble average (14 synthesis products) (black curve) • No substantial weakening associated with the 1976 “climate shift”: Wainwright et al. (2008) reported a 2.5-Sv reduction based on an analysis of IX1 XBT data (Fremantle – Sunda Strait). • Decadal signals of 10-15 year periods. • A consistent strengthening during 1992-2000: consistent with observed wind and SSH

17. Trend in Sea Level 1992-2001 (cm/yr) GECCO ECMWF SODA GECCO SODA ECMWF

18. GECCO ECMWF GECCO GECCO ECMWF ECMWF SODA SODA Trend in Sea Level 1962-2001 (cm/yr)

19. Next GSOP Efforts • Chairs: B. Sloyan, K. Haines (WOAP member), D. Stammer • Implementation of OO’09 Outcome (jointly with OOPC) • Reanalaysis of global historic hydrography • Reanalysis of XBT data • Analyze global budgets and sea level • EazyInit: Providing initial conditions for seasonal- to decadal predictions. • Improving initial conditions and initializations. • Preparing for Coupled Data assimilation

20. Thank you www.clivar.org