1. Xingren Wu and Robert Grumbine
Sea Ice
Xingren Wu and Robert Grumbine

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

5. NEMS/GFS Modeling Summer School
The Observed Arctic Sea Ice Extent (SIE): (
NEMS/GFS Modeling Summer School

6. NEMS/GFS Modeling Summer School
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 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. NEMS/GFS Modeling Summer School
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,
NEMS/GFS Modeling Summer School

12. NEMS/GFS Modeling Summer School
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. NEMS/GFS Modeling Summer School
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. NEMS/GFS Modeling Summer School
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. NEMS/GFS Modeling Summer School
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 dump for GDAS/CDAS):
FNACNA=“icegrb_file”
Sea ice climatology (from fix):
FNAISC=“/nwprod/fix/cfs_ice1x1monclim grb”
NEMS/GFS Modeling Summer School

16. NEMS/GFS Modeling Summer School
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_oi2sst1x1monclim 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. Sea-ice is one component of the CFS
GFS (LAND)
Time Step Δa
Fast loop: Δa= Δc= Δi
Slow loop: Δo Ts
Sea-Ice
Fluxes
Coupler
Time Step Δc
Atmosphere grid
X-grid
Ocean (MOM4)
Time Step Δo
Sea Ice
Time Step Δi
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
Sept 16, 2012
Feb 28, 2013
NEMS/GFS Modeling Summer School

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

23. NEMS/GFS Modeling Summer School
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)
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 hindcast climatology.
Sea ice extent and concentration
Extent
Concentration
Anom&Total
L0 L1 L2 L3 L4 L5 L6 L7 L8
NEMS/GFS Modeling Summer School

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

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

28. NEMS/GFS Modeling Summer School
Thank you!
CFSv2 data:
CFS Reanalysis data:
NEMS/GFS Modeling Summer School