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Impact of ALTIMETER and ARGO data in the new ECMWF ocean analysis system

Impact of ALTIMETER and ARGO data in the new ECMWF ocean analysis system. Magdalena A. Balmaseda Arthur Vidard David Anderson. Outline. The new ECMWF operational ocean analysis Historical reanalysis and real time The Observing System Experiments (OSEs) No ARGO No ALTIMETER NEITHER

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Impact of ALTIMETER and ARGO data in the new ECMWF ocean analysis system

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  1. Impact of ALTIMETER and ARGO data in the new ECMWF ocean analysis system Magdalena A. Balmaseda Arthur Vidard David Anderson Venice, 13-17 March 2006

  2. Outline • The new ECMWF operational ocean analysis • Historical reanalysis and real time • The Observing System Experiments (OSEs) • No ARGO • No ALTIMETER • NEITHER • Results • Summary and conclusions Venice, 13-17 March 2006

  3. Real time Probabilistic Coupled Forecast time Ocean reanalysis Consistency between historical and real-time initial initial conditions is required Quality of reanalysis affects the climatological PDF Main Objective: to provide ocean Initial conditions for coupled forecasts Coupled Hindcasts, needed to estimate climatological PDF, require a historical ocean reanalysis Venice, 13-17 March 2006

  4. System-3 • Ocean model: HOPE (~1x1) • Assimilation Method OI • Assimilation of T + Balanced relationships (T-S, ρ-U) • 10 days assimilation windows, increment spread in time • New Features • ERA-40 fluxes to initialize ocean • Retrospective Ocean Reanalysis back to 1959. • Multivariate on-line Bias Correction . • Assimilation of salinity data. • Assimilation of altimeter-derived sea level anomalies. • 3D OI Venice, 13-17 March 2006

  5. T/S conserved CH96 T/S conserved OI T/S Changed OI Assimilation of S(T) not S(z) Assimilation in the ECMWF operational system 3 Venice, 13-17 March 2006

  6. T/S conserved OI T/S Changed OI Assimilation of S(T) not S(z) System 3: Assimilation of Salinity Observations • Motivations: • Known drift in salinity • SofT scheme represents only the “ balanced” relatonship • Number of salinity data recently increased (ARGO) Idea: perform a second OI using T+S data to correct the T/S relationship (Haines et al 2006) Venice, 13-17 March 2006

  7. Assimilation of Salinity Contribution To ENACT: Assimilation of salinity along T surfaces (TM #458, Haines et al MWR) and are orthogonal Nice property: Venice, 13-17 March 2006

  8. T/S conserved T/S conserved OI CH96 T/S Changed OI Assimilation in ECMWF Operational System 3 Assimilation of S(T) not S(z) Venice, 13-17 March 2006

  9. Altimetry • Based on Cooper and Haines 1996 (basically translate SLA into increment of T and S) Ingredient: We tried ‘external’ mean sea level products (CLS, Nasa, …) but the choice of the reference global mean is not trivial and the system can be quite sensitive to this choice A Mean Sea Level Observed SLA from T/P+ERS+GFO Respect to 7 year mean of measurements Venice, 13-17 March 2006

  10. OI System3: Assimilation of Altimeter Data How to extract T/S information from Sea Level? How to combine Sea level and subsurface data? Cooper and Haines, 1999 Venice, 13-17 March 2006

  11. Data coverage for Nov 2005 Data coverage for June 1982 Changing observing system is a challenge for consistent reanalysis Today’s Observations will be used in years to come • ▲Moorings: SubsurfaceTemperature • ◊ ARGO floats: Subsurface Temperature and Salinity • + XBT : Subsurface Temperature Venice, 13-17 March 2006

  12. North Atlantic: T300 anomaly North Atlantic: S300 anomaly Climate Signals…. …or spurious trends due to changing observing system? Venice, 13-17 March 2006

  13. - = ARGO effect (with ALTI) ALL NO_ARGO = - ALTI effect (with ARGO) ALL NO_ALTI - = ARGO effect (with no ALTI) NO_ALTI NEITHER - = NO_ARGO NEITHER ALTI effect (with no ARGO) Observing System Experiments • Period 2001-2005: ALL NO_ARGO NEITHER NO_ALTI (no argo/no alti) Venice, 13-17 March 2006

  14. ALTIMER (With ARGO) ARGO (With altimeter) 2001-2005 Mean SSS ARGO (Without altimeter) ALTIMER (Without ARGO) OSES: Effect on Salinity Venice, 13-17 March 2006

  15. ALTIMER (with ARGO) ARGO (with altimeter) ARGO (without altimeter) ALTIMER (without ARGO) OSEs:Effect on Sea Level Venice, 13-17 March 2006

  16. Fit to the observations (rms error)Temperature Eastern Pacific South Pacific ALL NO_ALTI NO_ARGO NEITHER Venice, 13-17 March 2006

  17. Fit to the observations (rms error)Salinity Equatorial Indian Tropical Atlantic ALL NO_ALTI NO_ARGO NEITHER Venice, 13-17 March 2006

  18. Salinity Trend in North Atlantic Without ARGO, the salinity trend is half the size ALL NO_ALTI NO_ARGO NEITHER Venice, 13-17 March 2006

  19. Summary and Conclusions • The new ECMWF-S3 ocean analysis will be operational this year. • Historical reanalysis from 1959 to real time • Near real time ocean analysis (8 hours behind time) • Assimilation of Temperature, Salinity, and sea level from altimeter • Results from OSE experiments for the period 2001-2006: • Using Altimeter-derive sea level anomalies: • Improves the salinity field in the Indian Ocean • Improves the thermal structure in the Easten Equatorial Pacific • Improves the thermal representation in the Tropical and Equatorial Atlantic (not shown). • The Altimeter information benefits from the synergy with ARGO in regions where their effects overlap. ARGO has a large effect outside the tropics. • The representation of the North and South Atlantic remains a challenge. Venice, 13-17 March 2006

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