1. 1 Evaluation of two global HYCOM 1/12º hindcasts in the Mediterranean Sea Cedric Sommen 1 In collaboration with Alexandra Bozec 2 and Eric Chassignet 2 1 The French Military Academy of Saint-Cyr, Guer, France 2 Center for Ocean-Atmospheric Prediction Studies, Tallahassee, FL / 25

2. 2 Outline The Mediterranean Sea Presentation of the HYCOM global ocean prediction system Experimental set-up Circulation Temperature and Salinity Transport Comparison with ARGO profile Summary

3. 3 The Mediterranean Sea The Mediterranean Sea is a mid-latitude marginal sea connected to the Atlantic Ocean by the Gibraltar Strait. It has the particularity to produce dense (warm and salty) water that spreads into the Atlantic Ocean and thus can potentially have an impact on the global thermohaline circulation (Mauritzen and McCartney, 2001).

4. 4 The Mediterranean Outflow http://hycom.coaps.fsu.edu/thredds/dodC/gbl_simulation 1/12º Global HYCOM Hindcast for April, 16th 2007

5. 5 Presentation of the HYCOM global ocean prediction system Horizontal grid: 1/12° equatorial resolution 4500 x 3298 grid points, ~6.5 km spacing on average, ~3.5 km at pole Mercator 79°S to 47°N, then Arctic dipole patch Vertical coordinate surfaces: 32 for σ2* KPP mixed layer model Thermodynamic (energy loan) sea-ice model Surface forcing: FNMOC NOGAPS 0.5° wind stress, wind speed, thermal forcing, and NOGAPS 1.0° precipitation Monthly river runoff (986 rivers) Initialized from January climatology (GDEM3) T and S, then SSS relaxation from PHC 3.0 No subsurface relaxation to climatology

6. 6 Presentation of the HYCOM global ocean prediction system Sequential Incremental Update Cycle Analysis-Forecast-Analysis MVOI - simultaneous analysis 6 ocean variables temperature, salinity, geopotential, layer pressure, velocity (u,v) HYCOM Model Ocean QC 3D MVOI Ocean Obs SST: GAC/LAC MCSST, GOES, Ship, Buoy Profile: XBT, CTD, ARGO Floats, Fixed Buoy, Drifting Buoy Altimeter SSHA SSM/I Sea Ice Innovations Increments Forecast Fields Prediction Errors First Guess Navy Coupled Ocean Data Assimilation (NCODA)

7. 7 Goal of my study The main goal of this study is to determine if the 1/12º Hybrid Coordinate Ocean Model (HYCOM) global configuration is able to reproduce the main features of the Mediterranean circulation and its outflow in the Atlantic Ocean. In particular, we evaluate the ability of two hindcast simulations on the period June 2007 to September 2008

8. 8 EXPERIMENTAL SET-UP Hindcast 1 –Spin-up with climatological atmospheric reanalysis ERA15 1979- 1993. –Hindcast with 3-hourly 0.5º NOGAPS from Nov 2003-present. –Vertical projection of observed SSH using Cooper and Haines (1996). Hindcast 2 –Spin-up with climatological atmospheric reanalysis ERA40 1979- 2002 + winds scaled to Quikscat wind speed. –Hindcast with 3-hourly 0.5º NOGAPS + winds scaled to Quikscat wind speed from June 2007- present. –Vertical projection using synthetics temperature profiles from the Modular Ocean Data Assimilation System (MODAS) database.

9. 9 CIRCULATION In the eastern basin Hindcast 1Hindcast 2 (Hamad et al. 2005) Winter 2008 Current on Kinetic energy (m 2 /s 2 )

10. 10 CIRCULATION In the western basin Hindcast 1 Hindcast 2 (Millot et al. 1999) Current on Kinetic energy (m 2 /s 2 ) Winter 2008

11. 11 TEMPERATURE and SALINITY Temperature averaged over the whole water column Positive bias in Hindcast 1 Hindcast 2 stays closer to GDEM3 than Hindcast 1 EASTERN BASIN WESTERN BASIN

12. 12 TEMPERATURE and SALINITY Temperature Vertical sections: Eastern basin

13. 13 TEMPERATURE and SALINITY Salinity averaged over the whole water column Positive bias of Hindcast 1 in the eastern basin Slight positive bias in Hindcast 2 WESTERN BASIN EASTERN BASIN

14. 14 TEMPERATURE and SALINITY Vertical sections: Eastern basin Salinity

15. 15 TRANSPORT Experiments Transport (1Sv=10 6 m 3 /s) Salinity In/out (psu) Temperature In/Out (C) Observations~ 0.7-0.836.2/38.416.2/13. Gibraltar H10.63/-0.6236.2/38.016.6/13.8 Gibraltar H20.77/-0.7136.1/37.816.5/13.4 Observations1.10+/-0.58 38.70/37.513.8/15.4-16 Sicily H11.60/-1.7738.6/37.8 14.5/18.1 Sicily H21.0/-1.0238.3/37.65 15.1/16.9 Gibraltar strait Sicily strait

16. 16 COMPARISON WITH ARGO PROFILES In the eastern basin Temperature Anomaly GDEM3/ARGO: slight bias Hindcast 1/ARGO:worse than GDEM3 Hindcast 2/ARGO: improvement compared with GDEM3

17. 17 COMPARISON WITH ARGO PROFILES In the eastern basin Salinity Anomaly GDEM3/ARGO: fresh bias Hindcast 1/ARGO: too salty at the surface Hindcast 2/ARGO: improvement compared with GDEM3

18. 18 COMPARISON WITH ARGO PROFILES In the western basin Temperature Anomaly GDEM3/ARGO: slight cold bias Hindcast 1/ARGO:too warm Hindcast 2/ARGO:stays slightly too cold

19. 19 COMPARISON WITH ARGO PROFILES In the western basin Salinity Anomaly GDEM3/ARGO: fresh bias Hindcast 1/ARGO: too fresh Hindcast 2/ARGO: improvement compared with GDEM3

20. 20 SUMMARY The assimilation method using MODAS synthetics gives better results in the Mediterranean Sea than the Cooper-Haines assimilation method in terms of: large-scale Circulation pattern transport at the strait large and small scale T/S properties

21. 21 QUESTIONS ???