# Presentation: 162507

## 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**

## 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

## 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.

**Nilas & Leads**
**First-Year Ice**

**Multi-Year Ice**

**Melt Pond**

**Snow-Ice**

**Rafting**

**Pancake Ice**

**Greece Ice**

## Arctic sea-ice hits record low in 2007 

**NSIDC**

**9/16/2007**

## Sea-Ice in the Climate System

- A sea ice cover significantly reduces the amount of solar radiation absorbed at the earth’s 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**_

## Sea-Ice in the Climate System (cont.)

- 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.)**_

## IPCC, 1995

**IPCC, 1995**

## 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

## Sea-ice model and coupling issues

- Ice thermodynamics
- Ice dynamics
- Ice model coupling to the atmosphere
- Ice model coupling to the ocean

## 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)

## 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

- 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

_**Maykut and Untersteiner Model**_

## Ice Model: Dynamics

- Based on the principle of the conservation 	of momentum, determine:
-  Ice motions
-  Ice deformation
-  Leads (open water)

## 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

- 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

_**Hibler VP Model**_

## Sea-Ice in current operational CFS

- 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**_

## Sea-Ice in NCEP GFS (for NWP)

- 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)**_

## 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

## Sea-Ice in new CFS: dynamics 

**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, 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

## Sea-ice is one component of the new CFS

- Fluxes

- Tsfc
- Sea-Ice

- X-grid

- Slow loop: Δo

- Fast loop: Δa= Δc= Δi

_**Sea-ice is one component of the new CFS**_

## Tripolar grid of Murray (1996)

**This avoids a singularity at the North Pole**

_**Tripolar grid of Murray (1996)**_
_**over the Arctic for the sea-ice model**_

## Preliminary Results

**	****(1/3 in the tropics)**
**	****(**Δa= Δc= Δi=**10 min**, Δo=1hr)
**Sea-Ice Results**
**- Concentration**
**- Thickness**

_**Preliminary Results**_

## Arctic Sea-Ice Concentration

**March**

**CFS**
**20-year**

**95**
**90**
**80**
**60**
**40**
**20**

**OBS**

**95**
**90**
**80**
**60**
**40**
**20**

## Antarctic Sea-Ice Concentration

**September**

**OBS**

**95**
**90**
**80**
**60**
**40**
**20**

**CFS**
**20-year**

**95**
**90**
**80**
**60**
**40**
**20**

**Ice less compact**

## Annual Mean Arctic Sea-Ice Thickness

**Annual Mean Arctic Sea-Ice Thickness**

**CFS**
**20-year**

**Sea-ice thickness climatology based on pre-1985 data. (Bourke and Garrett, 1987). **

## Thank you!

**Thank you!**