2005 ROMS Users Meeting2005 ROMS Users MeetingMonday, October 24, 2005Monday, October 24, 2005

Coupled sea-ice/ocean Coupled sea-ice/ocean numerical simulations of the numerical simulations of the

Bering Sea for the period Bering Sea for the period 1996-present1996-present

Enrique Curchitser Enrique Curchitser Lamont Doherty Earth Observatory of Columbia U.Lamont Doherty Earth Observatory of Columbia U.

Al Hermann Al Hermann NOAA Pacific Marine Environmental LaboratoryNOAA Pacific Marine Environmental Laboratory

Kate Hedstrom Kate Hedstrom University of Alaska, FairbanksUniversity of Alaska, Fairbanks

Paul BudgellPaul Budgell Institute for Marine Research, Bergen, NorwayInstitute for Marine Research, Bergen, Norway

OutlineOutline• Motivation and backgroundMotivation and background

• Ocean and sea-ice model descriptionsOcean and sea-ice model descriptions

• Bering sea model implementationBering sea model implementation

• Results:Results:– CirculationCirculation– Sea-ice cover and thicknessSea-ice cover and thickness– Interannual variability and trendsInterannual variability and trends– Comparison to BarentsComparison to Barents

• Conclusions and future workConclusions and future work

MotivationMotivation

• A yardstick for climate change (sea A yardstick for climate change (sea ice)ice)

• High primary productivityHigh primary productivity

• Significant commercial fisheries Significant commercial fisheries (Pollock)(Pollock)

• Comparison with other sub-Arctic Comparison with other sub-Arctic seas (e.g., Barents)seas (e.g., Barents)

Ocean model: ROMSOcean model: ROMS• Hydrostatic, free surface primitive equation Hydrostatic, free surface primitive equation

modelmodel• Generalized terrain-following vertical Generalized terrain-following vertical

coordinatescoordinates• Boundary-fitted, orthogonal curvilinear Boundary-fitted, orthogonal curvilinear

horizontal coordinates on an Arakawa C-gridhorizontal coordinates on an Arakawa C-grid• Non-homogenous time-stepping algorithmNon-homogenous time-stepping algorithm• High-order advection schemesHigh-order advection schemes• Accurate baroclinic pressure gradient Accurate baroclinic pressure gradient • Continuous, monotonic reconstruction of Continuous, monotonic reconstruction of

vertical gradientsvertical gradients

Sea-ice modelSea-ice model

• Dynamics (Hunke and Duckowicz):Dynamics (Hunke and Duckowicz): – Elastic-viscous-plastic (EVP) rheology. Elastic-viscous-plastic (EVP) rheology.

Viscosities are linearized at every EVP time Viscosities are linearized at every EVP time step. EVP parallelizes very efficientlystep. EVP parallelizes very efficiently

• Thermodynamics (Mellor and Kantha; Thermodynamics (Mellor and Kantha; Hakkinen and Mellor): Hakkinen and Mellor): – Three-level, single layer ice; single snow layerThree-level, single layer ice; single snow layer– Molecular sub-layer under ice; Prandtl-type ice-Molecular sub-layer under ice; Prandtl-type ice-

ocean boundary layerocean boundary layer– Forcing by short- and long-wave radiation, Forcing by short- and long-wave radiation,

sensible and latent heat fluxessensible and latent heat fluxes

NEP NEP ImplementatioImplementation:n:• 10 km average 10 km average

horizontal resolutionhorizontal resolution• 30 vertical layers30 vertical layers• KPP vertical mixingKPP vertical mixing• IC’s and BC’s from IC’s and BC’s from

NPacNPac• NCEP daily mean NCEP daily mean

fluxes corrected for fluxes corrected for model surface model surface temperature and ice temperature and ice concentrationconcentration

• Modified short-wave Modified short-wave radiation flux radiation flux (important!)(important!)

Surface velocitiesSurface velocities

Transport in the passagesTransport in the passages

Unimak—Amukta--Bering

Sea ice concentration: January 1997Sea ice concentration: January 1997

ROMS SSM/I+

Sea ice concentration: January 1998Sea ice concentration: January 1998

ROMS SSM/I+

Sea ice concentration: January 2000Sea ice concentration: January 2000

ROMS SSM/I+

Sea ice concentration: January 2001Sea ice concentration: January 2001

ROMS

Sea ice concentration: March Sea ice concentration: March 1997/19981997/1998

1997 1998

Bering/Barents comparison of total ice Bering/Barents comparison of total ice covercover

BarentsBering

Model

“Data”

Sea ice thickness: January 1996/1997Sea ice thickness: January 1996/1997

1996 1997

Lessons from a “bad” simulation: The Lessons from a “bad” simulation: The global warming scenarioglobal warming scenario

NCEP (tweaked) NCEP

What is causing the variability What is causing the variability in the sea ice in the in the sea ice in the (Southeastern) Bering Sea?(Southeastern) Bering Sea?• Late formation (and early retreat) of Late formation (and early retreat) of

ice in the Arcticice in the Arctic

• Wind direction changeWind direction change

• Changes in Shortwave radiationChanges in Shortwave radiation

• Extra heat content on the shelf – Extra heat content on the shelf – e.g., more flow through Unimak passe.g., more flow through Unimak pass

Final remarks and further Final remarks and further workwork

• We implemented a coupled ocean/sea-ice regional We implemented a coupled ocean/sea-ice regional model for the Bering seamodel for the Bering sea

• The model reproduces the seasonal and The model reproduces the seasonal and interannual variability in the sea-ice conditions as interannual variability in the sea-ice conditions as well as the major circulation featureswell as the major circulation features

• The Bering sea shows similar ice trends as the The Bering sea shows similar ice trends as the BarentsBarents

• Future plans:Future plans:– Analyze the current simulation more carefully and…Analyze the current simulation more carefully and…– Higher resolution (~3km) implementation—important for a Higher resolution (~3km) implementation—important for a

better representation of the bathymetry and the Aleutian better representation of the bathymetry and the Aleutian passagespassages

– TidesTides– Couple an ecosystem modelCouple an ecosystem model

Sea ice concentration: January 1996Sea ice concentration: January 1996

ROMS SSM/I+