The dynamic-thermodynamic sea ice module in the

Bergen Climate ModelHelge Drange and Mats Bentsen

Nansen Environmental and Remote Sensing Center Bjerknes Centre for Climate Research

Zonal mean change in surface-T in 19 CMIP-models

http://www-pcmdi.llnl.gov/cmip

!

Reasons for model differences

• Different states of natural high-latitude climate variability modes

• Variations in sea ice extent in CTRL integration

• Actual winter sea ice extent in transient integration

Simulated change in surfacetemperature at 2xCO2 in

19 climate GCMs

Räisänen (2001), J. Climate, 14, 2088-2104

• Miami Isopycnic Coordinate Ocean Model (MICOM; Bleck et al., 1992) - a mixture of versions 2.6 to 2.8 is used• Dynamic-thermodynamic sea ice modules included• Reference pressure at the surface• 24 model layers with potential density ranging from 23.54 to 28.10• Stretched grids with focus in the North Atlantic-Arctic region (Bentsen et al., 1999)• Daily atmospheric forcing• Daily forcing from NCEP/NCAR reanalysis (Kalnay et al., 1996)• Period 1948 to present

• Many integrations conducted: - min 80, 40 and 20 km resolution, differing by different initial conditions only

MICOM-configuration

BCM-configuration, ARPEGE+MICOM• The atmospheric grid (red dots) has a resolution of T63 (2.8° by 2.8°), L31• The ocean grid (blue dots) has a resolution of 0.8° by 2.4° at the Equator,

gradually transforming to approximate square grid cells towards the poles (Mercator projection), L24 (MICOM v2.6-2.8 + dyn/thermodyn sea ice)

Old 300-yr BCM-CTRL: Sea ice thickness

Winter: Too thin but realistic extent in Arctic

Summer: Too thin and too small extent

March Sep

Simulated change in sea ice extent in old version of the Bergen Climate Model

Purple Control run White Doubled CO2

March September

Sea ice module

• Old: Treatment of heat fluxes in atmosphere coupled/uncoupled mode were different

• New: Heat fluxes split between solar and non-solar components, with temperature-dependent tendency term for non-solar component

• New: Improved conservation of heat and fresh water

• New: WENO advection scheme

• New: Bug fixes

Sea ice module in general

• Viscous-plastic rheology based on Hibler III (1979), based on the implementation of Harder (1996)

• 1 snow layer, 1 ice layer, linear temp profile in each layer

• Salinity-dependent freezing temperature

• Each grid cells accept ice and open water

• Metric terms included

0~ Hmgmf wauk

Sea ice thermodynamics

Short wave radiation

Albedo formulations

Exchange of heat between water and ice

fsrfcifmlwipww

boti TTfTTuCcQ

ST f 0.054715.273

If ,00 boti

boti QQ the is ice layer is melted (frozen) from below.

Ex: Computation of sea ice temperature

Simulated Arctic sea ice in the old version of NERSC-MICOM

Sea ice extent anomalies, obs and simulated

Lisæter et al.

Lisæter et al.

Sea ice thickness (m), obs and simulated

Sea ice thickness (m), obs and simulated

Lisæter et al.

Sea ice thickness (m), obs and simulated

Lisæter et al.

Simulated Arctic sea ice in the first version of NERSC-MICOM

Fairly realistic anomalies in sea ice thickness and extent

Too thin sea ice, in general (not shown)

Comparison: Old and new sea ice module

Sea ice thickness, monthly NCEP/NACR forcing

New

OldMarch

New

OldSeptember

Both versions produce realistic sea ice extent

Thickness distribution more realistic in new version

Sea ice concentration, monthly NCEP/NACR forcing

New

OldMarch

New

OldSeptember

Both versions produce realistic maximum sea ice extent

Concentration distribution more realistic in new version

Example from new BCM-integration (IPCC CTRL)

March September

New BCM control integration

Summary

New version of the sea ice module has been implemented and tested; improved numerics + conservation of heat and fresh water + bug fixes

Improved sea ice thickness and concentration distributions

Currently used for the new IPCC-simulations

300-yr CTRL: SST, SSS, Arctic and Antarctic sea ice extent