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The Global Ocean Data Assimilation System (GODAS) at NCEP: Introducing new data sets

The Global Ocean Data Assimilation System (GODAS) at NCEP: Introducing new data sets David Behringer Environmental Modeling Center, NCEP/NOAA Yan Xue Climate Prediction Center, NCEP/NOAA Office of Climate Observation (OCO) Annual System Review Silver Spring, Maryland, April 25-27, 2005.

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The Global Ocean Data Assimilation System (GODAS) at NCEP: Introducing new data sets

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  1. The Global Ocean Data Assimilation System (GODAS) at NCEP: Introducing new data sets David BehringerEnvironmental Modeling Center, NCEP/NOAAYan XueClimate Prediction Center, NCEP/NOAAOffice of Climate Observation (OCO) Annual System Review Silver Spring, Maryland, April 25-27, 2005

  2. Outline • The standard operational GODAS • Assimilating satellite altimetry • Assimilating Argo salinity profiles • The effect of a changing ocean observing system on • CFS S/I forecasts

  3. Seasonal to Interannual Forecasting at NCEP Ocean Initial Conditions Altimeter Argo Seasonal Forecasts for North America with Climate Atmosphere GCM SST XBT TAO Coupled Ocean Atmosphere Forecast System (CFS03) 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

  4. GODAS (MOM V.3) • Operational since September 2003 • Grid: • Quasi-global, 40 vertical levels. • Physics: • KPP boundary layer mixing scheme, • free surface. • Forcing: • Wind stress, heat flux, E-P from • Reanalysis 2 (R2), surface salinity • relaxed to Levitus monthly SSS • climatology. • Assimilation method: • 3D VAR, analyzes 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

  5. GODAS • Assimilation data sets Standard temperature and synthetic salinity Satellite altimetry data Argo salinity

  6. Ocean Observations Used in NCEP S/I Forecasting

  7. GODAS • Assimilation data sets Standard temperature and synthetic salinity Satellite altimetry data Argo salinity

  8. Assimilation of altimetry data • 2 Data sets TOPEX / Jason-1, 10-day period ERS-2 / Envisat, 35-day period Both acquired from AVISO through John Lillibridge (NESDIS) • 4 Experiments GTSE - assimilates temperature, synthetic salinity and TOPEX / Jason-1, 1993-2003 GTSEn - assimilates temperature, synthetic salinity and ERS-2 / Envisat, 1996-2003 GTS - assimilates temperature and synthetic salinity GSIM - control, no assimilation

  9. 12 / 28 / 1997 - 1 / 07 / 1998 12 / 14 / 1997 - 1 / 18 / 1998

  10. RMS COR SIM 9.96 0.54 GTS 4.88 0.88 GTSE 3.27 0.93 GTSEn 2.87 0.96 SIM 6.65 0.54 GTS 4.50 0.82 GTSE 3.22 0.90 GTSEn 3.42 0.90 SIM 4.85 0.80 GTS 2.94 0.93 GTSE 2.22 0.96 GTSEn 2.30 0.97

  11. RMS COR SIM 5.06 0.85 GTS 5.30 0.81 GTSE 4.38 0.88 GTSEn 4.02 0.93 SIM 5.35 0.81 GTS 3.58 0.91 GTSE 3.07 0.94 GTSEn 3.17 0.96 SIM 4.38 0.88 GTS 2.73 0.96 GTSE 2.10 0.97 GTSEn 1.97 0.98

  12. GODAS • Assimilation data sets Standard temperature and synthetic salinity Satellite altimetry data Argo salinity

  13. Assimilation of Argo salinity • Each temperature profile (XBT, mooring, Argo) is paired with a salinity profile • XBT and mooring profiles are paired with synthetic salinity profiles • Most Argo profiles are paired with observed salinity profiles • Synthetic salinity profiles are assigned larger errors based on the statistics of the synthetic - observed profile differences • The experiment runs from the beginning of 2000 through the end of 2004

  14. Operational SI prediction • GODAS runs daily producing a daily mean file and a restart file that lag the current date by 8 days. • CFS runs 2x daily, initialized by the GODAS restart file and the R2 atmospheric analysis. • Each forecast extends out to 9 months. • The ensemble forecast is built from the forecasts run on 20 consecutive days for a total of 40 members.

  15. Courtesy of Dr Peitao Peng

  16. Courtesy of Dr Peitao Peng

  17. Summary • Assimilation of new data sets • Altimetry assimilation leads to general improvement in GODAS sea level. It’s impact on CFS predictions is to be determined. • Assimilation of Argo salinity leads to a general improvement in GODAS salinity. There is less improvement in western tropical Pacific and near river outflows. • S/I forecasting • The CFS S/I forecasts show higher skill in the 1990s than in the 1980s. • The likely cause is a shift in the GODAS climatology that in turn is due changes in the assimilation data set.

  18. Data Availability on the Internet • GODAS Analyses • Operational GODAS fields (5-day and monthly ave) sea surface height surface temperature and salinity surface isothermal and mixed layer depths heat content of upper 300 meters temperature, salinity and currents at 40 levels surface forcing (wind-stress, heat flux, E-P) • Reanalysis, 5-day averages, 1979-present • Operational, weekly, rotating archive, ftp://ftpprd.ncep.noaa.gov:cmb/Products/G3R2TSo

  19. The End

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