Multi-decadal Coupled Sea-ice/Ocean Numerical

Simulations of the Bering Sea

Kate Hedstrom, ARSC/UAFEnrique Curchitser, LDEO

Al Hermann, PMELJanuary, 2006

Bering Sea

• Motivation and background• Bering sea model implementation• Results:

– Circulation– Sea-ice cover– Interannual variability and trends

• Conclusions and future work

Motivation

• A yardstick for climate change (sea ice)

• High primary productivity• Significant commercial fisheries (Pollock)

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

The Model• ROMS ocean

– F90– Now with an adjoint and tangent linear for

data assimilation

• Ice model from Paul Budgell– EVP dynamics (Arakawa C grid)– Mellor-Kantha thermodynamics– Oceanic molecular sublayer under the ice

for improved behavior

NEP Implementation

• 10 km average horizontal resolution• Run1:

– 30 vertical layers– IC’s and BC’s from NPac– Daily fluxes from NCEP hindcast (modified)– 1996-2002, 1960-1970

• Run2:– 42 vertical layers– IC’s and BC’s from CCSM (POP)– Six-hourly fluxes from CCSM hindcast– 1958-2000+, up to 1974 so far

Surface velocities - NCEP

Sea ice concentration: January 1996

ROMS - NCEP SSM/I+

Sea ice concentration: January 1997

ROMS - Run 1

SSM/I+

Sea ice concentration: January 1998

ROMS - Run 1

SSM/I+

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

NCEP (tweaked)

NCEP

Sea Surface Temperature

ROMS - NCEP ROMS - CCSM

Sea-ice Concentration: April 1966

ROMS - NCEP ROMS - CCSM

Sea-ice Concentration: April 1969

ROMS - NCEP ROMS - CCSM

Sea-ice Concentration: April 1963

ROMS - NCEP ROMS - CCSM

Future Plans

• Finish the 10 km run driven by CCSM forcing

• Run on the 4 km grid– Four tidal constituents from Mike Forman– Closer to eddy resolving– Estimate 200 hours/year on 48 pwr4 processors

• Add an ecosystem model (and modeler)

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

• The CCSM forcing fields are a significant improvement:– Higher time resolution– No hack to the heat fluxes

• We hope to use these simulations to improve our understanding of the circulation and ecosystem in the Bering Sea

Surface Velocityweekly means 1960-1963