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USCGC Healy Cruise

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Title: USCGC Healy Cruise Author: dlamb Last modified by: hlpan Created Date: 3/7/2002 2:32:53 PM Document presentation format: On-screen Show Company – PowerPoint PPT presentation

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Title: USCGC Healy Cruise


1
The 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
2
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
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
Pancake Ice
Multi-Year Ice
Greece Ice
Melt Pond
Snow-Ice
Rafting
4
NSIDC
Arctic sea-ice hits record low in 2007
9/16/2007
5
Sea-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.

6
Sea-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.

7
IPCC, 1995
8
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
  • Sea-ice model and coupling issues
  • Ice thermodynamics
  • Ice dynamics
  • Ice model coupling to the atmosphere
  • Ice model coupling to the ocean

10
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
Maykut 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
12
Ice Model Dynamics
  • Based on the principle of the conservation of
    momentum, determine
  • Ice motions
  • Ice deformation
  • Leads (open water)

13
Hibler 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
14
Sea-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).

15
Sea-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.

16
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
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, 1997. An
elastic-viscous-plastic model for sea ice
dynamics. J. Phys. Oceanogr., 27, 1849-1867
18
Sea-ice is one component of the new CFS
Fast loop ?a ?c ?i
Slow loop ?o
Fluxes
Tsfc Sea-Ice
X-grid
19
Tripolar grid of Murray (1996) over the Arctic
for the sea-ice model
This avoids a singularity at the North Pole
20
Preliminary 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

21
Arctic Sea-Ice Concentration March
CFS 20-year
95 90 80 60 40 20
OBS
95 90 80 60 40 20
22
Antarctic Sea-Ice Concentration September
95 90 80 60 40 20
CFS 20-year
95 90 80 60 40 20
OBS
Ice less compact
23
Annual Mean Arctic Sea-Ice Thickness
CFS 20-year
Sea-ice thickness climatology based on pre-1985
data. (Bourke and Garrett, 1987).
24
Thank you!
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