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