Imposed versus Dynamically Modeled Sea

Ice:A ROMS study of the effects on

polynyas and waters masses in the Ross Sea

John M. Klinck, Y. Sinan Hüsrevoglu and Michael S.

Dinniman Center for Coastal Physical

Oceanography Old Dominion University

Introduction

Sea ice is important for ocean surface fluxes and water transformations at high latitude.

Imposed sea ice is easier and has some accuracy.

Atmosphere, ocean and ice can be inconsistent.

Can not represent dynamics of polynyas or variation from observed conditions.

Questions

What is the sensitivity of dynamic sea ice to forcing and OBC?

How realistic are sea ice results for the Ross Sea compared to observations?

What is the influence of Terra Nova Bay Polynya on High Salinity Shelf Water?

Model Overview• ROMS v2.1 primitive equation model• 5 km grid spacing• Includes silicate and nitrate with

simplified uptake• Includes water under Ross Ice Shelf• Daily wind stress for years 2000 and 2001• Surface fluxes from bulk formulae and

surface atmospheric conditions• Imposed and dynamic (CICE) sea ice • Additional information by Mike Dinniman.

Sea Ice Model

• CICE V3.1 (Hunke and Dukowicz, 1997:2002)

• 5 ice categories with 4 layers in each category (cat 4, 5 are rare).

• One snow layer• Same grid as ocean model ( point is

common)• Changed tiling and data structure to that

of ROMS.

Coupling

•WRF I/O API MCT (V 2.0.1) Coupling Implementation (Weather Research and Forecasting) (Model Coupling Toolkit)•Loose Coupling (1 hr step)•Spherical Coordinate Remapping and Interpolation Package (SCRIP) from LANL to map between C-grid (ROMS) and B-grid (CICE)•Freezing/Melting potential calculated by ROMS (algorithm of CCSM, not Steele et al 1989)•CICE/CSIM data structure converted to ROMS tiling.

Domain

•Thin lines are isobaths•Shaded area is under Ross Ice Shelf•Black line is section for later figures

Forcing

• Atmospheric forcing from ECMWF.• Daily values of wind, air temp, pressure,

humidity and clouds for 2000 and 2001.• Daily precipitation is from NCEP/NCAR

reanalysis.• Added winds from Terra Nova Bay AWS at

two points in ECMWF grid (called AWS case).

Annual Average wind stress

2000

2001

AWS ECMWF

Open Boundaries• T and S specified by WOA 01 monthly

climatology (radiation+adaptive nudging)• Integrated transport from OCCAM

(radiation+adaptive nudging)• Radiation for baroclinic flow• Monthly SSM/I climatology for ice

concentration on eastern boundary (imposed+nudging area)

• Ice thickness is 30 cm for ECMWF and 50 cm for AWS

Forcing and Coupling

Ocean only

Flow diagram

MPI barrier at symbols

Results Shown

Zonal salinity section in FebruaryMonthly average ice concentrationInterannual differences in ice concentration

and thicknessRelative importance of dynamics and

thermodynamicsTerra Nova Bay effect on salinityBottom salinity

Salinity year 4

Higher salinity with dynamic sea ice

Too much salinity

Convection over bathymetry

Mixed layer thickness?

Ice Concentration Nov 2000AWS ECMWF

Climatology SSM/I

Ice Concentration Dec 2000

OBC

Ice Concentration Jan 2001

Annual Average Ice

2000

2001

AWS forcing

Annual Average Ice processes for 2001

Thermodynamic growth, dynamic loss shows polynyas.

Dynamic growth at north shows OBC problem

Bottom Salinity

Initial Year 3

Bottom Salinity

Year 3 Climatology

AWS wind effect on Terra Nova Bay (year 3)

HSSW

Effect may be too much due to expanded area

Conclusions

• Small scale winds important for polynyas• Ice open boundary conditions need good

information• Dynamic sea ice produces more salt than

imposed sea ice.• HSSW is created and drains to shelf break

as expected.

The End

The BEDMAP data were provided courtesy of the BEDMAP consortium. Computer facilities and support were

provided by the Commonwealth Center for Coastal Physical

Oceanography. This work was supported by the U.S. National Science Foundation Grants OCE-99-11731 and OPP-03-37247.

Ice Concentration Jan 2001

Ice Concentration Dec 2001

Ice Concentration, Nov 2001AWS ECMWF

climatology SSM/I obs

Salinity year 2

Salinity year 3

Tnb year 2

Tnb year 1

Winds near Terra Nova

Bay

Black arrows are NCEP/QSCAT

Red arrow is AWS station