Impact of ARGO data in the ECMWF (System 3) operational ocean analysis system

1. Impact of ARGO data in the ECMWF (System 3) operational ocean analysis system Magdalena A. Balmaseda Arthur Vidard David Anderson AST, Paris 8 March 2007

2. Outline • The S3 ECMWF operational ocean analysis • Historical reanalysis and real time • ARGO coverage and quality control • The Observing System Experiments (OSEs) • No ARGO (temperature and salinity) • No Altimeter • NO ARGO and NO Altimeter • Results • Impact on the ocean analysis and on the seasonal forecasts • Summary and conclusions AST, Paris 8 March 2007

3. ECMWF: Weather and Climate Dynamical Forecasts 10-Day Medium-Range Forecasts Seasonal Forecasts Monthly Forecasts Atmospheric model Atmospheric model Wave model Wave model Ocean model Real Time Ocean Analysis ~8 hours Delayed Ocean Analysis ~11 days AST, Paris 8 March 2007

4. 1 2 3 4 5 6 7 8 9 10 11 12 BRT ocean analysis: D1-12 NRT ocean analysis: D1 Time (days) Assimilation at D1-12 Assimilation at D1-5 Operational Ocean Analysis Schedule D1 • BRT ( Behind real time ocean analysis): ~12 days delay • For seasonal Forecasts. • Continuation of the historical ocean reanalysis • NRT (Near real time ocean analysis):~ No delay • For Monthly forecasts AST, Paris 8 March 2007

5. 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 and global sea level trends. • 3D OI AST, Paris 8 March 2007

6. T/S conserved T/S conserved OI CH96 T/S Changed OI Idea: perform a second OI using T+S data to correct the T/S relationship Assimilation of S(T) not S(z) Assimilation of different data streams • Sequential assimilation • S(T) and not S(z) • Gestrophic velocity increments. AST, Paris 8 March 2007

7. 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 AST, Paris 8 March 2007

8. Bias evolution vector-equation ¢ = + f f b b b ; - k k k 1 b k (Temperature,Salinity,Velocity) prescribed (constant/seasonal) Some notation AST, Paris 8 March 2007

9. 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 AST, Paris 8 March 2007

10. North Atlantic: T300 anomaly North Atlantic: S300 anomaly Climate Signals…. …or spurious trends due to changing observing system? AST, Paris 8 March 2007

11. ARGO in the Real time analysis • The data arrives within 24 hours. • ~1/3 of the data is partially rejected by the QC • Most of the partially rejected profiles are in the Atlantic • The rejection is due to large difference with the background field. • Could it be the SOLO floats? • An experiment has been run with the SOLO floats blacklisted • The impact of the SOLO floats is very small in the ECMWF analysis, probably because they were rejected. AST, Paris 8 March 2007

12. - = ARGO effect (with ALTI) ALL NO_ARGO = - ALTI effect (with ARGO) ALL NO_ALTI = - - = ARGO effect (with no ALTI) Salinity effect (~ ARGO) NO_ALTI ALL NO_SAL NO_AA - = NO_ARGO NO_AA ALTI effect (with no ARGO) Observing System Experiments • Period 2001-2006: ALL NO_ARGO NO_SAL NO_AA NO_ALTI AST, Paris 8 March 2007

13. OSES: Effect on Surface Salinity Effect of ARGO Effect of Salinity AST, Paris 8 March 2007

14. Effect on Salinity averaged upper 300m AST, Paris 8 March 2007

15. Effect of Argo on T300 Most of it is due to direct effect of ARGO temperature AST, Paris 8 March 2007

16. Effect on Sea Level When altimeter If no altimeter AST, Paris 8 March 2007

17. Fit to the observations (rms error)Temperature Eastern Pacific South Pacific ALL NO_ALTI NO_ARGO NO_AA AST, Paris 8 March 2007

18. Fit to the observations (rms error)Salinity Tropical Indian Equatorial Atlantic ALL NO_ALTI NO_ARGO NO_AA AST, Paris 8 March 2007

19. Impact on the skill of Seasonal Forecasts Small but significant improvement. In several regions AST, Paris 8 March 2007

20. Summary • ARGO data arrives timely (within 24 hours) • ARGO data is partially rejected in the Atlantic by the automatic QC procedure. • Black lists of defective instruments are very useful • Both ARGO temperature and salinity have a large information content. • The ARGO data is best used in combination with the altimeter information. • Using ARGO data in the initialization of seasonal forecasts has a positive impact on the skill of SST predictions. The impact is small but consistent, and it is significant in some regions. AST, Paris 8 March 2007