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 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 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 earths surface. Nilas & Leads First-Year Ice Multi-Year Ice Melt PondSnow-Ice Rafting Pancake Ice Greece Ice CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Arctic sea-ice hits record low in 2007 NSIDC 9/16/2007 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 earths 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 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.) CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model IPCC, 1995 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 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 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) 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 Some results from a time-dependent thermodynamic model of sea ice. J. Geophys. Res., 76, Maykut and Untersteiner Model 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) 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 A dynamic thermodynamic sea ice model. J. Phys. Oceanogr., 9, Hibler VP Model 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 CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model A three-layer thermodynamic sea-ice model has been embedded into GFS since May 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) 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 A reformulated three-layer sea ice model. J. Atmos. Ocean. Tech., 17(4), 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 Hiblers viscous-plastic (VP) model Computionally more efficient than Hiblers VP model, suitable for fully coupled models Hunke, E. C. and J. K. Dukowicz, An elastic-viscous-plastic model for sea ice dynamics. J. Phys. Oceanogr., 27, CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Sea-Ice Time Step i GFS (LAND) Time Step a Ocean Time Step o Coupler Time Step c Fluxes Tsfc Sea-Ice X-grid Slow loop : o Fast loop: a= c= i Atmosphere grid Sea-ice is one component of the new CFS 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 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) (a= c= i=10 min, o=1hr) Sea-Ice Results - Concentration - Thickness Preliminary Results CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Arctic Sea-Ice Concentration March CFS 20-year OBS CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Antarctic Sea-Ice Concentration September OBS CFS 20-year Ice less compact 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). CFSRR: 11/7/2007Xingren Wu: The Sea-Ice Model Thank you!