Ocean Reanalysis D. Stammer

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, ….). 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

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.

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).

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

(Trenberth et al.) Improved Heat Content Estimate

Domingues et al. (2008) Global Heat Content Anomaly (10 22 J)

No Model z-Level Model EN3 DePreSys MIT MOM POPOPA/NEMO ERA40 NCEP Mercator URDG SODA GFDL GODAS K-7 HOPE ECMWF INGV 3D-Var/OI 4D-Var.25 o x.25 o 1 o x1 o 2 o x2 o CORE GECCO Bias corr. E-P. Relax. QSCAT GPCP DATA

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.

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

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

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

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

Global Synthesis and Observations Panel Intercomparison of the Indonesian Throughflow (ITF) Transport Estimated by Ocean Data Assimilation (ODA) Products (Joint GSOP-IOP activity) 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 year periods. A consistent strengthening during : consistent with observed wind and SSH Five-year low-pass ITF transport anomaly (color curves) and their ensemble average (14 synthesis products) (black curve)

SODA ECMWF GECCO SODAECMWF GECCO Trend in Sea Level (cm/yr)

SODA ECMWF GECCO SODA ECMWF GECCO Trend in Sea Level (cm/yr)

Next GSOP Efforts Chairs: B. Sloyan, K. Haines ( WOAP member ), D. Stammer Implementation of OO’09 Outcome (jointly withOOPC) 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

Thank you