a regional ice-ocean simulation of the barents and kara seas w. paul budgell

A Regional Ice-Ocean SimulationOf the Barents and Kara Seas

W. Paul Budgell

Institute of Marine Researchand

Bjerknes Centre for Climate ResearchBergen, Norway

ROMS User Meeting, VeniceOctober 18-21, 2004

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Outline of Talk:

• Background

• Description of ice-ocean model

• Model set-up

• Simulation results • Comparison with observations

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BackgroundRegion of interest is the Barents SeaDynamical downscaling experimentsFirst replicate present-day climate

Validate with available observations

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Model Domain

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Ocean Model Component

• Community Regional Ocean Modelling System (ROMS) version 2.1

• Terrain-following coordinate system with generalized vertical coordinate, curvilinear coordinates in horizontal

• Wide variety of mixing schemes available

• Advanced numerics, OMP and MPI parallel.

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Ocean Model Component

• Used 3rd-order upwind-biased horizontal advection

• Used piece-wise parabolic splines in vertical, spline vertical advection, spline Jacobian baroclinic pressure gradient at topography

• Used GLS mixing with MY2.5 parameters

• No explicit horizontal viscosity or diffusivity

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Ice Dynamics

Ice dynamics are based upon the elastic-viscous-plastic (EVP)rheology of Hunke and Dukowicz (1997), Hunke (1991) and Hunke and Dukowicz (1992).

Under low deformation (rigid behaviour), the singularity is regularized by elastic waves. The response is very similar toviscous-plastic models in typical Arctic pack ice conditions.

Numerical behaviour improved significantly by applyinglinearization of the viscosities at every EVP time step.

The EVP model parallelizes very efficiently under both OpenMPAnd MPI.

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Ice Thermodynamics

Ice thermodynamics are based upon those of Mellor andKantha (1989) and Häkkinen and Mellor (1992). Main featuresinclude:• Three-level, single layer ice; single snow layer• Molecular sublayer under ice; Prandtl-type ice-ocean boundary layer• Surface melt ponds• Forcing by short and long-wave radiation, sensible and latent heat flux• NCEP fluxes, corrected for model surface temperature and ice concentration, used as forcing

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Model Set-up

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Model Set-up

• Horizontal resolution of 7.8 to 10.5 km, average of 9.3 km

• 32 levels in the vertical

• Flather (free surface) and Chapman (momentum) open boundary conditions for 2D variables

• Nudging + radiation condition OBCs for 3D-mom and tracers

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Boundary and Initial Conditions

• Tidal forcing from AOTIM

• Coarse model used for initialization and boundary forcing of regional model

• 50 km resolution in Nordic Seas/Arctic

• NCEP daily mean fluxes (Bentsen and Drange, 2001) used for forcing

• Hindcast from 1948-2002 completed, archived 5-day mean fields

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Results are shown from the first yearof a1990-2002 simulation

SST Ice Concentration

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Comparison with observations:

SST from PODAAC Pathfinder AVHRRbest SST, ascending (day-time) orbit,8-day, 9-km means

Ice concentration from SSM/I passive micowave, daily means

Bjørnøya-Fugløya CTD sections

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SST

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Sea Ice Concentration

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Section Locations

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T - Bjørnøya-Fugløya Section - March

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T - Bjørnøya-Fugløya Section – Sept.

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S - Bjørnøya-Fugløya Section – Sept.

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Brine Drainage Spitzbergen Section

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Brine Drainage W. Novoya Zemlya Section

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Ice Production - 1993

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Ice Melt - 1993

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Conclusions

• Model captures seasonal variability in the Barents • Good agreement with observed ice distribution

• Barents inflow is too cold, too fresh – OBC issue

• Brine rejection from ice formation produces realistic water masses

• ROMS captures significant portion of mesoscale variability even with 9-km resolution