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D. W. Behringer NOAA / NCEP The Second Argo Science Workshop Venice, Italy 18 March 2006

The impact of Argo temperature and salinity data on the NCEP Global Ocean Data Assimilation System (GODAS). D. W. Behringer NOAA / NCEP The Second Argo Science Workshop Venice, Italy 18 March 2006. Seasonal to Interannual Forecasting at NCEP. Ocean Initial Conditions. Altimeter. Argo.

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D. W. Behringer NOAA / NCEP The Second Argo Science Workshop Venice, Italy 18 March 2006

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  1. The impact of Argo temperature and salinity data on the NCEP Global Ocean Data Assimilation System (GODAS) D. W. Behringer NOAA / NCEP The Second Argo Science Workshop Venice, Italy 18 March 2006

  2. Seasonal to Interannual Forecasting at NCEP Ocean Initial Conditions Altimeter Argo Seasonal Forecasts for North America with CFS SST XBT TAO Coupled Ocean Atmosphere Forecast System (CFS) CCA, OCN MR, ENSO Global Ocean Data Assimilation System (GODAS) IRI SST Anomaly Surface Temperature & Rainfall Anomalies Stress Heat Fluxes CCA, CA Markov IRI Forecasters E-P Official Probabilistic Surface Temperature & Rainfall Forecasts Scatterometer Official SST Forecast

  3. GODAS (MOM V.3) • Operational since September 2003 • Grid: • Quasi-global, 1x1 degree horizontal • resolution, enhanced to 1/3 degree • in the tropics, 40 vertical levels. • Physics: • KPP boundary layer mixing scheme, • free surface. • Forcing: • Wind stress, heat flux, E-P from • Reanalysis 2 (R2), SST relaxed to • weekly Reynolds’ analysis, SSS • relaxed to Levitus monthly climatology. • Assimilation method: • 3D VAR, univariate in temperature • and salinity, error covariance varies • geographically and temporally. • Assimilation data: • Temperature profile data from XBTs, • profiling floats (Argo), moorings • (TAO), synthetic salinity constructed • from temperature and local Levitus • T-S climatology. CFS03 Operational since August 2004 Atmosphere: T62/64-layer version of the current NCEP atmospheric Global Forecast System (GFS) with the same configuration as used in R2 Ocean: GFDL Modular Ocean Model (MOM V. 3) with the same configuration as used in GODAS Coupling: Direct coupling with no flux correction, accomplished daily

  4. The question: Does the addition of Argo salinity data improve the representation of the ocean state in GODAS?

  5. GODAS Experiments • GDS - operational version, assimilates temperature from XBTs (xT), Argo (aT) and TAO/Triton/PIRATA (tT) and synthetic salinity (sS) • GDSA - assimilates xT, aT, tT, sS and Argo salinity (aS) • GDSAX - assimilates xT, sS, aT and aS • RA6 - Previous operational system, Pacific Ocean only, assimilates xT, aT, and tT, but NOT salinity • CON - control, model is configured as in GDS, but there is no data assimilation

  6. GODAS Experiments • GDS - operational version, assimilates temperature from XBTs (xT), Argo (aT) and TAO/Triton/PIRATA (tT) and synthetic salinity (sS) • GDSA - assimilates xT, aT, tT, sS and Argo salinity (aS) • GDSAX - assimilates xT, sS, aT and aS • RA6 - Previous operational system, Pacific Ocean only, assimilates xT, aT, and tT, but NOT salinity • CON - control, model is configured as in GDS, but there is no data assimilation Comparison of cross-equatorial model sections with independent CTD sections.

  7. A comparison of the synthetic salinity profiles as used in the operational GODAS with Argo salinity profiles.

  8. GODAS Experiments • GDS - operational version, assimilates temperature from XBTs (xT), Argo (aT) and TAO/Triton/PIRATA (tT) and synthetic salinity (sS) • GDSA - assimilates xT, aT, tT, sS and Argo salinity (aS) • GDSAX - assimilates xT, sS, aT and aS • RA6 - Previous operational system, Pacific Ocean only, assimilates xT, aT, and tT, but NOT salinity • CON - control, model is configured as in GDS, but there is no data assimilation Comparison of temperature and salinity profiles from GODAS experiments with Argo profiles.

  9. GODAS Experiments • GDS - operational version, assimilates temperature from XBTs (xT), Argo (aT) and TAO/Triton/PIRATA (tT) and synthetic salinity (sS) • GDSA - assimilates xT, aT, tT, sS and Argo salinity (aS) • GDSAX - assimilates xT, sS, aT and aS • RA6 - Previous operational system, Pacific Ocean only, assimilates xT, aT, and tT, but NOT salinity • CON - control, model is configured as in GDS, but there is no data assimilation Comparison of temperature and salinity profiles from GODAS experiments with Argo profiles.

  10. GODAS Experiments • GDS - operational version, assimilates temperature from XBTs (xT), Argo (aT) and TAO/Triton/PIRATA (tT) and synthetic salinity (sS) • GDSA - assimilates xT, aT, tT, sS and Argo salinity (aS) • GDSAX - assimilates xT, sS, aT and aS • RA6 - Previous operational system, Pacific Ocean only, assimilates xT, aT, and tT, but NOT salinity • CON - control, model is configured as in GDS, but there is no data assimilation Comparison of cross-equatorial model sections with independent CTD sections.

  11. GODAS Experiments • GDS - operational version, assimilates temperature from XBTs (xT), Argo (aT) and TAO/Triton/PIRATA (tT) and synthetic salinity (sS) • GDSA - assimilates xT, aT, tT, sS and Argo salinity (aS) • GDSAX - assimilates xT, sS, aT and aS • RA6 - Previous operational system, Pacific Ocean only, assimilates xT, aT, and tT, but NOT salinity • CON - control, model is configured as in GDS, but there is no data assimilation Correlations and RMS differences of model SSH with TOPEX / Jason-1 SSH.

  12. Concluding Remarks • The experiments described here can provide only a very preliminary look at the impact of Argo on the NCEP GODAS. Over the 2000-2005 integration period of the experiments, the Argo array has only approached full global coverage during the last 2 years. In that same period, there has not been a significant ENSO event. Although several more years of assimilating Argo data will be needed before more definitive conclusions can be drawn, the following preliminary remarks are possible. • The assimilation the Argo salinity data, which are not part of the operational GODAS data set, produces a measurable improvement in the GODAS salinity field. • The Argo network is indispensable as a replacement for a shrinking XBT network. However, its coverage of the tropical Pacific is not sufficient for it to act as a substitute for the TAO/TRITON array.

  13. Concluding Remarks cont’d • In the 2000-2005 time period the assimilation of temperature alone (RA6) improves the representation of SSH relative to the Control in the tropical Pacific. The assimilation of both temperature and salinity (GDS, GDSA) leads to some additional improvement west of the dateline in the tropical Pacific. • A remaining question is whether adding new data sets to the operational GODAS will have an impact on the NCEP S/I forecasts. A definitive answer to this question will be possible only after a period of many years (O~20) spanning several ENSO events. Any conclusions drawn from retrospective forecasts over a shorter period of time would not be statistically reliable. In the interim, the best strategy remains to continue improving the model and the assimilation method to make the best possible use of the available data.

  14. The End cfs.ncep.noaa.gov/cfs/godas www.cpc.ncep.noaa.gov/products/GODAS

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