Title: USCGC Healy Cruise
1The Sea-Ice Model
Xingren Wu EMC/NCEP/NOAA
Acknowledgements all EMC/NCEP members, in
particular, Dave Behringer, Robert Grumbine,
Yu-tai Hou, Mark Irredel, Steve Lord, Kenneth
Mitchell, Shrinivas Moorthi, Hua-Lu Pan, Diane
Stokes, Suranjana Saha, Jiande Wang, Jun Wang
2Outline
- 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
3Sea 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
Pancake Ice
Multi-Year Ice
Greece Ice
Melt Pond
Snow-Ice
Rafting
4NSIDC
Arctic sea-ice hits record low in 2007
9/16/2007
5Sea-Ice in the Climate System
- 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.
6Sea-Ice in the Climate System (cont.)
- 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.
7IPCC, 1995
8Issues 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- Sea-ice model and coupling issues
- Ice thermodynamics
- Ice dynamics
- Ice model coupling to the atmosphere
- Ice model coupling to the ocean
10Ice 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)
11Maykut and Untersteiner 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
12Ice Model Dynamics
- Based on the principle of the conservation of
momentum, determine - Ice motions
- Ice deformation
- Leads (open water)
13Hibler VP 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
14Sea-Ice in current operational CFS
- 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).
15Sea-Ice in NCEP GFS (for NWP)
- 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.
16Sea-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
17Sea-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, 1997. An
elastic-viscous-plastic model for sea ice
dynamics. J. Phys. Oceanogr., 27, 1849-1867
18Sea-ice is one component of the new CFS
Fast loop ?a ?c ?i
Slow loop ?o
Fluxes
Tsfc Sea-Ice
X-grid
19Tripolar grid of Murray (1996) over the Arctic
for the sea-ice model
This avoids a singularity at the North Pole
20Preliminary Results
- Experiment GFS T126L64 coupled to 1x1 degree of
sea-ice and ocean - (1/3 in the tropics)
- (?a ?c ?i10 min, ?o1hr)
- Sea-Ice Results
- - Concentration
- - Thickness
21Arctic Sea-Ice Concentration March
CFS 20-year
95 90 80 60 40 20
OBS
95 90 80 60 40 20
22Antarctic Sea-Ice Concentration September
95 90 80 60 40 20
CFS 20-year
95 90 80 60 40 20
OBS
Ice less compact
23Annual Mean Arctic Sea-Ice Thickness
CFS 20-year
Sea-ice thickness climatology based on pre-1985
data. (Bourke and Garrett, 1987).
24Thank you!