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Coupled sea-ice/ocean numerical simulations of the Bering Sea for the period 1996-present

Coupled sea-ice/ocean numerical simulations of the Bering Sea for the period 1996-present. Enrique Curchitser Lamont Doherty Earth Observatory of Columbia U. Al Hermann NOAA Pacific Marine Environmental Laboratory Kate Hedstrom University of Alaska, Fairbanks Paul Budgell

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Coupled sea-ice/ocean numerical simulations of the Bering Sea for the period 1996-present

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  1. Coupled sea-ice/ocean numerical simulations of the Bering Sea for the period 1996-present Enrique Curchitser Lamont Doherty Earth Observatory of Columbia U. Al Hermann NOAA Pacific Marine Environmental Laboratory Kate Hedstrom University of Alaska, Fairbanks Paul Budgell Institute for Marine Research, Bergen, Norway 2005 ROMS Users Meeting

  2. Outline • Motivation and background • Ocean and sea-ice model descriptions • Bering sea model implementation • Results: • Circulation • Sea-ice cover and thickness • Interannual variability and trends • Comparison to Barents • Conclusions and future work

  3. Motivation • A yardstick for climate change (sea ice) • High primary productivity • Significant commercial fisheries (Pollock) • Comparison with other sub-Arctic seas (e.g., Barents)

  4. Ocean model: ROMS • Hydrostatic, free surface primitive equation model • Generalized terrain-following vertical coordinates • Boundary-fitted, orthogonal curvilinear horizontal coordinates on an Arakawa C-grid • Non-homogenous time-stepping algorithm • High-order advection schemes • Accurate baroclinic pressure gradient • Continuous, monotonic reconstruction of vertical gradients

  5. Sea-ice model • Dynamics (Hunke and Duckowicz): • Elastic-viscous-plastic (EVP) rheology. Viscosities are linearized at every EVP time step. EVP parallelizes very efficiently • Thermodynamics (Mellor and Kantha; Hakkinen and Mellor): • Three-level, single layer ice; single snow layer • Molecular sub-layer under ice; Prandtl-type ice-ocean boundary layer • Forcing by short- and long-wave radiation, sensible and latent heat fluxes

  6. 10 km average horizontal resolution 30 vertical layers KPP vertical mixing IC’s and BC’s from NPac NCEP daily mean fluxes corrected for model surface temperature and ice concentration Modified short-wave radiation flux (important!) NEP Implementation:

  7. Surface velocities

  8. Transport in the passages Unimak—Amukta--Bering

  9. Sea ice concentration: January 1997 ROMS SSM/I+

  10. Sea ice concentration: January 1998 ROMS SSM/I+

  11. Sea ice concentration: January 2000 ROMS SSM/I+

  12. Sea ice concentration: January 2001 ROMS

  13. Sea ice concentration: March 1997/1998 1997 1998

  14. Bering/Barents comparison of total ice cover Bering Barents Model “Data”

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

  16. Lessons from a “bad” simulation: The global warming scenario NCEP (tweaked) NCEP

  17. What is causing the variability in the sea ice in the (Southeastern) Bering Sea? • Late formation (and early retreat) of ice in the Arctic • Wind direction change • Changes in Shortwave radiation • Extra heat content on the shelf – e.g., more flow through Unimak pass

  18. Final remarks and further work • We implemented a coupled ocean/sea-ice regional model for the Bering sea • The model reproduces the seasonal and interannual variability in the sea-ice conditions as well as the major circulation features • The Bering sea shows similar ice trends as the Barents • Future plans: • Analyze the current simulation more carefully and… • Higher resolution (~3km) implementation—important for a better representation of the bathymetry and the Aleutian passages • Tides • Couple an ecosystem model

  19. Sea ice concentration: January 1996 ROMS SSM/I+

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