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Evaluation of two global HYCOM 1/12º hindcasts in the Mediterranean Sea

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. Outline.

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Evaluation of two global HYCOM 1/12º hindcasts in the Mediterranean Sea

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  1. Evaluation of two global HYCOM 1/12º hindcasts in the Mediterranean Sea Cedric Sommen1 In collaboration with Alexandra Bozec2 and Eric Chassignet2 1 The French Military Academy of Saint-Cyr, Guer, France 2 Center for Ocean-Atmospheric Prediction Studies, Tallahassee, FL / 25

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

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

  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. 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. CIRCULATION (Hamad et al. 2005) • In the eastern basin Winter 2008 Current on Kinetic energy (m2/s2) Hindcast 1 Hindcast 2

  10. CIRCULATION (Millot et al. 1999) • In the western basin Winter 2008 Current on Kinetic energy (m2/s2) Hindcast 1 Hindcast 2

  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 WESTERN BASIN EASTERN BASIN

  12. TEMPERATURE and SALINITY Temperature Vertical sections: Eastern basin

  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. TEMPERATURE and SALINITY Salinity Vertical sections: Eastern basin

  15. TRANSPORT Gibraltar strait Sicily strait

  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. 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. 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. 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. 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. QUESTIONS???

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