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Sea Ice

Sea Ice. Xingren Wu and Robert Grumbine. 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. Pancake Ice. Nilas & Leads First-Year Ice. Greece Ice. Multi-Year Ice. Melt Pond. Snow-Ice. Rafting.

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Sea Ice

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  1. Sea Ice Xingren Wu and Robert Grumbine

  2. 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. Pancake Ice Nilas & Leads First-Year Ice Greece Ice Multi-Year Ice Melt Pond Snow-Ice Rafting NEMS/GFS Modeling Summer School

  3. Sea ice affects climate and weatherrelated processes • Sea ice amplifies any change of climate due to its “positive feedback” (coupled climate model concern): Sea ice is white and reflects solar radiation back to space. More sea ice cools the Earth, less of it warms the Earth. A cooler Earth means more sea ice and vice versa. • Sea ice restricts the exchange of heat/water between the air and ocean (NWP concern) • Sea ice modifies air/sea momentum transfer, ocean fresh water balance and ocean circulation: The formation of sea ice injects salt into the ocean which makes the water heavier and causes it to flow downwards to the deep waters and drive a massive ocean circulation NEMS/GFS Modeling Summer School

  4. Arctic/Antarctic Sea Ice Concentration: The Cryosphere Today(arctic.atmos.uiuc.edu/cryosphere) NEMS/GFS Modeling Summer School

  5. The Observed Arctic Sea Ice Extent (SIE):(www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm) NEMS/GFS Modeling Summer School

  6. Minimum Arctic Sea Ice (1982 and 2012)The Cryosphere Today: (arctic.atmos.uiuc.edu/cryosphere) NEMS/GFS Modeling Summer School

  7. Arctic SIE Anomalies for Sept: NSIDC(from 1979-2000 mean) Arctic minimum SIE has decreased more than 45% since 1979 NEMS/GFS Modeling Summer School

  8. Issues related to sea ice and sea ice forecast • Data assimilation • Sea ice concentration data are available but velocity data lack to real time • Lack of sea ice and snow thickness data • Initial conditions • Sea ice concentration data are available but velocity data lack to real time • Sea ice and snow thickness data are based on model spinup values or climatology • Sea ice models and coupling • Ice thermodynamics/Ice dynamics • Ice model coupling to the atmosphere/ocean NEMS/GFS Modeling Summer School

  9. Ice Model: Thermodynamics • Based on the principle of the conservation of energy, determine: • Ice formation • Ice growth • Ice/snow melting • Ice/snow temperature structure NEMS/GFS Modeling Summer School

  10. Ice Model: Dynamics • Based on the principle of the conservation of momentum, determine: • Ice motions • Ice deformation • Leads (open water) NEMS/GFS Modeling Summer School

  11. Sea Ice in the NCEP Global Forecast System • A three-layer thermodynamic sea ice model (Winton 2000) was implemented into GFS in May 2005. • It predicts sea ice/snow thickness, the surface temperature and ice temperature structure. • In each model grid box, the heat and moisture fluxes and albedo are treated separately for ice and open water. Winton, M. 2000: A reformulated three-layer sea ice model, J. of Atmospheric and Oceanic Technology, 17, 525-531. NEMS/GFS Modeling Summer School

  12. Sea Ice in the NCEP GFS -> +----------+ <- ts - diagnostic surface temperature ( <= 0C ) / | | hs | snow | <- 0-heat capacity snow layer \ | | => +---------+ / | | / | | <- t1 - upper 1/2 ice temperature; this layer has / | | a variable (T/S dependent) heat capacity hi | ...ice... | \ | | \ | | <- t2 - lower 1/2 ice temp. (fixed heat capacity) \ | | -> +----------+ <- base of ice fixed at seawater freezing temp. SEA ICE THERMODYNAMIC STRUCTURE (Winton 2000) NEMS/GFS Modeling Summer School

  13. Sea Ice in the NCEP GFS Atmospheric Model Ice Fraction SW Heat Flux LW Heat Flux Turbulent Heat Flux Snow Rate Ice Fraction Ice/Snow Thickness Ice/Snow Thickness 3-layer thermodynamics Ice Model Ice Temperature Ice Temperature surface Temperature Surface Temperature Salinity Oceanic Heat Flux Fresh Water [Ocean Model] NEMS/GFS Modeling Summer School

  14. Sea Ice in the NCEP GFS • The surface T is determined from the diagnostic balance of the heat fluxes (Conductive, short- and longwave radiation, and sensible and latent heat fluxes). • The ice T (upper and lower layers) is calculated based on conservation of enthalpy. • If the calculated surface T is greater than the freezing T of snow or sea ice the surface T is fixed at the melting T of snow or sea ice, and the ice T is recomputed. The residual energy flux is applied toward surface melting of snow or sea ice. • At the ice/water interface, the conservation of energy dictates that the energy absorbed or released through melting (or freezing) balances the oceanic heat flux to the ice bottom and the conductive flux of heat upward from the bottom. NEMS/GFS Modeling Summer School

  15. Sea Ice in the NCEP GFS • The analyzed fractional ice cover is kept unchanged during the entire forecast period in GFS, but there is an option to use climatology for daily sea ice concentration. • Sea ice analysis (0.5x0.5 grib file from dumpfor GDAS/CDAS): • FNACNA=“icegrb_file” • Sea ice climatology (from fix): • FNAISC=“/nwprod/fix/cfs_ice1x1monclim19822001.grb” NEMS/GFS Modeling Summer School

  16. SST in the NCEP GFS • Current operation: • SST Analysis (1x1 in GFS; 0.25x0.25 in CFS from dump): • FNTSFA=“sstgrb_file” • SST climatology (from fix): • FNTSFC=“/nwprod/fix/cfs_oi2sst1x1monclim19822001.grb” • Future implementation: • Higher resolution SST will be tested in the new GFS NEMS/GFS Modeling Summer School

  17. Temperature bias over 90oN-60oN for January 2004 (T62/L64) Negative bias decreases NEMS/GFS Modeling Summer School

  18. Sea Ice in the CFS (GFDL Sea Ice Simulator - SIS) • 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 • 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 NEMS/GFS Modeling Summer School

  19. Ocean (MOM4) Time Step Δo Coupler Time Step Δc GFS (LAND) Time Step Δa Sea Ice Time Step Δi Atmosphere grid Sea-ice is one component of the CFS Fast loop:Δa= Δc= Δi Slow loop: Δo Fluxes Ts Sea-Ice X-grid NEMS/GFS Modeling Summer School

  20. Sea Ice “Assimilation” in CFSR/CFSv2 • When sea ice concentration is greater than (or equal to) 15% from observation, sea ice concentration is reset to the observed value in the guess field. New ice can occur in this case. • In summer, the melt pond effect on ice albedo is considered in the Arctic. • When sea ice concentration is less than 15% from observation, sea ice in the guess field will be removed (treated to melt). • Quality control has been used to prevent sea ice from the warmer water. (Ice analysis and SST analysis feedback) NEMS/GFS Modeling Summer School

  21. Sea Ice “Assimilation” in CFSR/CFSv2 www.emc.ncep.noaa.gov/gc_wmb/wd20xw/cfsrr/index.html Sept 16, 2012 Feb 28, 2013 NEMS/GFS Modeling Summer School

  22. Sea Ice in the CFS Reanalysis (CFSR) Sea-ice concentration Arctic Antarctic (monthly mean) 198709 over fixed area: 197909 sea-ice Near Record minimum sea-ice in Sept 2007 over fixed area: 197902 sea-ice 200709 NEMS/GFS Modeling Summer School

  23. Surface air temperature from CFSR (Sept) and the difference amongst CFSR, R1, R2 and ERA40 Cold bias in R1: 1.7K than obs CFSR is: 1.8K Warmer than R1 NEMS/GFS Modeling Summer School

  24. Sept sea ice concentration in CFSR and CFSv2 hindcast NEMS/GFS Modeling Summer School

  25. Seasonal Sea Ice Forecast from CFSv2:CPC (Wanqiu Wang) www.cpc.ncep.noaa.gov/products/people/wwang/cfsv2fcst/ Jan 2014 with Apr 2013 ICs Forecasts are from initial conditions of the last 10 days, with 4 runs from each day. Forecast ensembles consist of 40 members from initial a period of 10 days. Anomalies are with respect to 1982-2010 hindcast climatology. Sea ice extent and concentration NEMS/GFS Modeling Summer School

  26. 2012 Sea Ice Outlook for the MinimumArctic Sea Ice Extent: August Report (SEARCH) NEMS/GFS Modeling Summer School From SEARCH: Study of Environmental Arctic Change

  27. 2013 Sea Ice Outlook for the MinimumArctic Sea Ice Extent: June Report (SEARCH) NEMS/GFS Modeling Summer School From SEARCH: Study of Environmental Arctic Change

  28. Thank you! CFSv2 data: http://cfs.ncep.noaa.gov CFS Reanalysis data: http://nomads.ncdc.noaa.gov/NOAAReanalysis/cfsrr NEMS/GFS Modeling Summer School

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