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The dynamic-thermodynamic sea ice module in the Bergen Climate Model

The dynamic-thermodynamic sea ice module in the Bergen Climate Model. Helge Drange and Mats Bentsen Nansen Environmental and Remote Sensing Center Bjerknes Centre for Climate Research. !. Zonal mean change in surface- T in 19 CMIP-models. Reasons for model differences

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The dynamic-thermodynamic sea ice module in the Bergen Climate Model

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  1. The dynamic-thermodynamic sea ice module in the Bergen Climate Model Helge Drange and Mats Bentsen Nansen Environmental and Remote Sensing Center Bjerknes Centre for Climate Research

  2. ! Zonal mean change in surface-T in 19 CMIP-models • Reasons for model differences • Different states of natural high-latitude climate variability modes • Variations in sea ice extent in CTRL integration • Actual winter sea ice extent in transient integration http://www-pcmdi.llnl.gov/cmip

  3. Simulated change in surface temperature at 2xCO2 in 19 climate GCMs Räisänen (2001), J. Climate, 14, 2088-2104

  4. MICOM-configuration • Miami Isopycnic Coordinate Ocean Model (MICOM; Bleck et al., 1992) - a mixture of versions 2.6 to 2.8 is used • Dynamic-thermodynamic sea ice modules included • Reference pressure at the surface • 24 model layers with potential density ranging from 23.54 to 28.10 • Stretched grids with focus in the North Atlantic-Arctic region (Bentsen et al., 1999) • Daily atmospheric forcing • Daily forcing from NCEP/NCAR • reanalysis (Kalnay et al., 1996) • Period 1948 to present • Many integrations conducted: • - min 80, 40 and 20 km resolution, • differing by different initial • conditions only

  5. BCM-configuration, ARPEGE+MICOM • The atmospheric grid (red dots) has a resolution of T63 (2.8° by 2.8°), L31 • The ocean grid (blue dots) has a resolution of 0.8° by 2.4° at the Equator, gradually transforming to approximate square grid cells towards the poles (Mercator projection), L24 (MICOM v2.6-2.8 + dyn/thermodyn sea ice)

  6. Old 300-yr BCM-CTRL: Sea ice thickness March Sep Winter: Too thin but realistic extent in Arctic Summer: Too thin and too small extent

  7. September Simulated change in sea ice extent in old version of the Bergen Climate Model Purple Control run White Doubled CO2 March

  8. Sea ice module • Old: Treatment of heat fluxes in atmosphere coupled/uncoupled mode were different • New: Heat fluxes split between solar and non-solar components, with temperature-dependent tendency term for non-solar component • New: Improved conservation of heat and fresh water • New: WENO advection scheme • New: Bug fixes

  9. Sea ice module in general • Viscous-plastic rheology based on Hibler III (1979), based on the implementation of Harder (1996) • 1 snow layer, 1 ice layer, linear temp profile in each layer • Salinity-dependent freezing temperature • Each grid cells accept ice and open water • Metric terms included

  10. Sea ice thermodynamics

  11. Short wave radiation

  12. Albedo formulations

  13. Exchange of heat between water and ice If the is ice layer is melted (frozen) from below.

  14. Ex: Computation of sea ice temperature

  15. Simulated Arctic sea ice in the old version of NERSC-MICOM

  16. Sea ice extent anomalies, obs and simulated Lisæter et al.

  17. Sea ice thickness (m), obs and simulated Lisæter et al.

  18. Sea ice thickness (m), obs and simulated Lisæter et al.

  19. Sea ice thickness (m), obs and simulated Lisæter et al.

  20. Simulated Arctic sea ice in the first version of NERSC-MICOM Fairly realistic anomalies in sea ice thickness and extent Too thin sea ice, in general (not shown)

  21. Comparison: Old and new sea ice module

  22. Sea ice thickness, monthly NCEP/NACR forcing New New September Old Old Both versions produce realistic sea ice extent Thickness distribution more realistic in new version March

  23. Sea ice concentration, monthly NCEP/NACR forcing New New September Old Old Both versions produce realistic maximum sea ice extent Concentration distribution more realistic in new version March

  24. Example from new BCM-integration (IPCC CTRL)

  25. New BCM control integration March September

  26. Summary New version of the sea ice module has been implemented and tested; improved numerics + conservation of heat and fresh water + bug fixes Improved sea ice thickness and concentration distributions Currently used for the new IPCC-simulations

  27. 300-yr CTRL: SST, SSS, Arctic and Antarctic sea ice extent

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