Role of Assimilation of ARGO Data in the Improvement of Tropical Pacific Ocean Simulations

1. Role of Assimilation of ARGO Data in the Improvement of Tropical Pacific Ocean Simulations E. Hackert, J. Ballabrera-Poy, A. Busalacchi and R. Murtugudde Second ARGO Workshop, March 16-18

2. Model and Forcing • Reduced-gravity, primitive equation, sigma coordinate model [Gent and Cane, 1989] • Hybrid variable depth mixed layer [Chen et al., 1994] • Advective AML coupled to OGCM [Seager et al., 1995] • Realistic coastlines for tropical Pacific (124oE-280oE, 30oN-30oS), 20 layers • Forcing: • COAPS Objective Analysis wind stress • Xie and Arkin + GPCP rainfall anomalies added to ISCCP seasonal cycle • NCEP reanalysis clouds • ERBE solar radiation

3. MULTIVARIATE REDUCED ORDER KALMAN FILTER Truncation of error covariance: Kalman filter analysis equation: Ensemble estimate Parameterization truncation error

4. Assimilation Data • Tz and Sz - Global Temperature-Salinity Profile Program (GTSPP) “best copy” data set [NODC, 2006]

5. GTSPP Data • Continually managed database – real time and delayed mode temperature and salinity profiles – no duplicates • Includes XBT, CTD, TAO, ARGO, etc. data • Keep only “good”, “probably good” or “modified” data • Correct for known XBT fall rate errors [UNESCO, 1994] • GTSPP tests – location, gradient, climate, and consistency • Conventional Subsurface Data - CSD = all data platforms except ARGO and TAO

6. Temperature # ARGO OBS > CSD Salinity

7. Equator band lacks ARGO Observations Equator well sampled by CSD Temperature 2001 2005

8. Salinity Salinity -sparse data coverage in 2001 2001 Salinity data coverage - improved significantly in 2005 due to ARGO 2005

9. RMS Difference – Assimilation results versus TAO Observations Temperature Salinity

10. Assimilate more observations – better agreement with TAO Temperature # ARGO OBS > CSD Salinity

11. Assimilation of ARGO + CSD outperforms both ARGO and CSD ARGO assimilation performs well in western and central basin CSD assimilation performs better in east Data Assimilated Correlation – assimilation results versus observed SL ARGO+CSD ARGO CSD

12. ARGO ARGO has lower RMSD with observations then CSD in west at depth of thermocline ARGO has higher RMSD in Nino3 region at surface Data Assimilated RMSD – assimilation results versus observed Equatorial TAO T(xz) OI ARGO+CSD ARGO CSD

13. NINO3 SST’ versus time Poor NINO3 simulation corresponds to lack of observations in waveguide Number of superobs within 5o band for ARGO versus time

14. Adding TAO to assimilation • Can we improve simulation by adding a limited number of observations within waveguide?

15. Data Assimilated Adding few waveguide observations improves simulation Correlation assimilation results versus observed SL ARGO + TAO ARGO

16. Data Assimilated Adding TAO improves El Nino signal in east RMSD – assimilation results versus observed Equatorial TAO T(xz) OI ARGO + TAO ARGO

17. What is Contribution of Salinity?

18. Data Assimilated Inclusion of salinity improves SL correlation in central Pacific Correlation assimilation results versus observed SL ARGO Tz+SZ ARGO Tz

19. Data Assimilated Inclusion of salinity in assimilation reduces error with TAO observations in western Pacific at depth of thermocline RMSD – assimilation results versus observed Equatorial TAO T(xz) OI ARGO Tz+SZ ARGO Tz

20. Conclusions • Combined assimilation (ARGO + CSD) gives best overall simulation • More data improves simulation - ARGO after 2003 • Assimilation of CSD data improves in east whereas ARGO improves in the west – suboptimal performance of ARGO in the east due to lack of data in wave-guide for 2002 El Nino • Assimilation of ARGO Sz improves other variables including SL’ and Tz especially in the west (poor performance of CSD in west partially due to lack of salinity observations)

21. Supplemental Slides

22. Kelvin-Rossby Signal from isolation of forcing 2001-2002

25. Correlation assimilation results versus observed SL RMSD – model versus observed Equatorial TAO T(xz) OI