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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