1. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model The Sea-Ice Model Xingren Wu EMC/NCEP/NOAA Acknowledgements: all EMC/NCEP members, in particular, Dave Behringer, Robert Grumbine,Yu-tai Hou, Dave Behringer, Robert Grumbine, Yu-tai Hou, Mark Irredel,Steve Lord, Kenneth Mitchell, Mark Irredel, Steve Lord, Kenneth Mitchell, Shrinivas Moorthi, Hua-Lu Pan, Diane Stokes, Suranjana Saha, Jiande Wang, Jun Wang

2. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Outline  Sea-ice  Sea-ice in the climate system  Sea-ice thermodynamics and dynamics  Sea-ice in NCEP operational CFS  Sea-ice in NCEP GFS  Sea-ice models  Sea-ice in NCEP new CFS

3. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Sea Ice Sea ice is a thin skin of frozen water covering the polar oceans. It is a highly variable feature of the earth’s surface. Nilas & Leads First-Year Ice Multi-Year Ice Melt PondSnow-Ice Rafting Pancake Ice Greece Ice

4. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Arctic sea-ice hits record low in 2007 NSIDC 9/16/2007

5. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Sea-ice interacts strongly with both the atmosphere above and the ocean underneath in high latitudes. A sea ice cover significantly reduces the amount of solar radiation absorbed at the earth’s surface due to the marked changes in the surface albedo. The presence of extensive areas of sea ice suppresses heat loss by the ocean. The extent of sea ice is mainly influenced by, and has a significant effect on, the energy budget at the surface, and ocean-air energy exchange. Sea-Ice in the Climate System

6. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model The relationship between climate and sea ice is complex. Sea ice responds rapidly and sensitively to climatic change due to its “positive feedback”. Snow on sea ice is also a very important factor in shaping polar climate. In view of the varied impacts of the atmosphere, ocean and sea ice on each other, it is therefore important to include the sea-ice process in our weather and climate models. Sea-Ice in the Climate System (cont.)

7. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model IPCC, 1995

8. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Issues related to sea-ice in GFS and CFS  Data assimilation and Initial conditions  Sea-ice models and coupling Initial condition issues Sea-ice concentration data are available  Sea-ice thickness and velocity data are based on model spin-up values, so is snow thickness

9. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Sea-ice model and coupling issues  Ice thermodynamics  Ice dynamics  Ice model coupling to the atmosphere  Ice model coupling to the ocean

10. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Ice Model: Thermodynamics Based on the principle of the conservation of energy, determine: Ice formation Ice growth Ice/snow melting Ice/snow temperature structure Leads (open water)

11. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model 1D vertical high-resolution sea-ice model Effects of snow cover, ice salinity, and internal heating due to penetration of solar radiation Thermodynamics of heat conduction through sea-ice between the atmosphere and the ocean Sea-ice formation and decay Maykut, G.A. and N. Untersteiner. 1971. Some results from a time-dependent thermodynamic model of sea ice. J. Geophys. Res., 76, 1550-1575 Maykut and Untersteiner Model

12. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Ice Model: Dynamics Based on the principle of the conservation of momentum, determine: Ice motions Ice deformation Leads (open water)

13. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Five major dynamic forces in the momentum equation: –air stress at the top of sea-ice –water stress below sea-ice –gravitational stress from the tilt of sea surface (dynamic topography) –coriolis force –pressure stresses within ice Nonlinear viscous-plastic (VP) ice rheology Hibler, W.D.III. 1979. A dynamic thermodynamic sea ice model. J. Phys. Oceanogr., 9, 815-846 Hibler VP Model

14. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Sea-ice is treated in a simple manner - 3 m depth with 100% concentration (i.e. no open water within the ice covered area). The surface temperature is predicted based on energy balance at the ice surface. Sea-ice climatology is used to update sea-ice change in CFS (with 50% cutoff for sea-ice cover). Sea-Ice in current operational CFS

15. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model A three-layer thermodynamic sea-ice model has been embedded into GFS since May 2005. Sea-ice concentration is prescribed. Sea-ice/snow thickness, the surface temperature and ice temperature structure are predicted. The heat and moisture fluxes and albedo are treated separately for ice and open water. Sea-Ice in NCEP GFS (for NWP)

16. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Sea-Ice in new CFS: thermodynamics Winton (2000) 3-layer thermodynamic model plus ice thickness distribution 2-layer of sea-ice and 1-layer of snow Fully implicit time-stepping scheme, allowing longer time steps ➢ 5 categories of sea-ice Winton, M. 2000. A reformulated three-layer sea ice model. J. Atmos. Ocean. Tech., 17(4), 525-531

17. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Sea-Ice in new CFS: dynamics Hunke and Dukowicz (1997) elastic-viscous- plastic (EVP) ice dynamics model ➢ Improved numerical method for Hibler’s viscous-plastic (VP) model ➢ Computionally more efficient than Hibler’s VP model, suitable for fully coupled models Hunke, E. C. and J. K. Dukowicz, 1997. An elastic-viscous-plastic model for sea ice dynamics. J. Phys. Oceanogr., 27, 1849-1867

18. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Sea-Ice Time Step Δi GFS (LAND) Time Step Δa Ocean Time Step Δo Coupler Time Step Δc Fluxes Tsfc Sea-Ice X-grid Slow loop : Δo Fast loop: Δa= Δc= Δi Atmosphere grid Sea-ice is one component of the new CFS

19. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model This avoids a singularity at the North Pole Tripolar grid of Murray (1996) over the Arctic for the sea-ice model

20. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Experiment: GFS T126L64 coupled to 1x1 degree of sea-ice and ocean (1/3 in the tropics) (Δa= Δc= Δi=10 min, Δo=1hr) Sea-Ice Results - Concentration - Thickness Preliminary Results

21. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Arctic Sea-Ice Concentration March CFS 20-year 95 90 80 60 40 20 OBS 95 90 80 60 40 20

22. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Antarctic Sea-Ice Concentration September OBS 95 90 80 60 40 20 CFS 20-year 95 90 80 60 40 20 Ice less compact

23. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Annual Mean Arctic Sea-Ice Thickness CFS 20-year Sea-ice thickness climatology based on pre-1985 data. (Bourke and Garrett, 1987).

24. CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Thank you!