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Ocean component of Community Climate System Model , v4.

Ocean component of Community Climate System Model , v4. Peter Gent Ex - Chairman CCSM Scientific Steering Committee. WHAT’S NEW IN CCSM4 OCEAN COMPONENT? (since CCSM3). Increased vertical resolution (60-levels); 10m to ~200m,

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Ocean component of Community Climate System Model , v4.

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  1. Ocean component of Community Climate System Model , v4. Peter Gent Ex - Chairman CCSM Scientific Steering Committee

  2. WHAT’S NEW IN CCSM4 OCEAN COMPONENT? (since CCSM3) • Increased vertical resolution (60-levels); 10m to ~200m, • Modified anisotropic horizontal viscosity scheme, and background diffusion and viscosity in KPP (Jochum et al.), • Near-surface eddy flux parameterization with transition layer between ML and deep (Danabasoglu, Ferrari, et al.), • Vertically-varying isopycnal and thickness diffusivities; decrease in deeper ocean (Danabasoglu and J. Marshall), • Tidally driven mixing scheme (Jayne et al.), • Sub-mesoscale parameterization (Fox-Kemper et al.), • Overflow parameterization (Danabasoglu, Large, Briegleb), • Passive tracer (ideal age, CFCs) and ecosystem code are in.

  3. Near-surface eddy flux scheme (Danabasoglu, Ferrari & McWilliams 2008) EDDY-INDUCED MERIDIONAL OVERTURNING (GLOBAL) CONTROL NSEF Vertical profile of zonally-integrated total advective heat flux at 49oS

  4. BOTTOM TOPOGRAPHY OF THE x1 RESOLUTION OCEAN MODEL

  5. ATLANTIC MERIDIONAL OVERTURNING CIRCULATION (Sv) Ocean-only control Ocean-only w/ overflows Coupled control Coupled w/ overflows 170-year long ocean-only (normal-year forcing) and coupled CCSM4 simulations with 2o FV atmosphere and x1 ocean.

  6. TEMPERATURE AND SALINITY DIFFERENCES FROM OBSERVATIONS AT 2.65-km DEPTH mean= 0.45oC rms= 0.50oC mean= -0.04oC rms= 0.13oC Ocean-only control Ocean-only w/ overflows oC mean= 0.02 psu rms= 0.03 psu mean= -0.03 psu rms= 0.03 psu Obs: Levitus et al. (1998), Steele et al. (2001) psu

  7. ENSO CHARACTERISTICS OBSERVATIONS HadiSST 1966 - 2005 1o CCSM 4 1850 - 1921

  8. SST DIFFERENCES FROM OBSERVATIONS mean= -0.06oC rms= 1.29oC mean= 0.63oC rms= 1.44oC mean= -0.01oC rms= 1.07oC Obs: Levitus et al. (1998), Steele et al. (2001) oC

  9. Ocean Initialization for Decadal Forecasts • Used 2 datasets: hindcast using the CCSM 3.5 ocean component, and the GFDL ocean reanalysis product. • Have tried 2 methods: a) initialize ocean and run, b) strongly restore to hindcast over 5-10 yrs, then run. • In all cases, the N Atlantic MOC returned to near its coupled run value in 4-5 years. Hindcast or GFDL? • BIG DIFFERENCE - CCSM 4 runs do not have the large ~20 year period MOC oscillation that was in CCSM 3. • Using Data Assimilation Research Testbed to produce an ocean reanalysis using CCSM 4 (J. Anderson et al).

  10. Future Developments • Evaluate whether to move to HYPOP as base code: Tracer eqn uses z near surface, isopycnals in deep. • If stay with POP, then need to abandon constant volume and virtual salinity surface fluxes. • Improvement in coastal regions, including interactions with shelf circulations, river outflows, and ice shelves. • Downscaling and upscaling between CCSM ocean and ROMS run at considerably higher spatial resolution. • Continue to develop eddy-resolving implementations.

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