Sea Ice Deformation in a Coupled Sea Ice-Ocean Model and from Satellite Remote Sensing: Comparison and Model Adaptation

Sea Ice Deformation Studies and Model DevelopmentGunnar Spreen, Han Tran, Ron Kwok, and Dimitris Menemenlis #1OverviewRegional Arctic setup with optimized parameters from 18 km integration (Green's function approach): Nguyen et al. (2011), JGR

Regional Arctic solution 4.5, 9 and 18 km horizontal grid spacing. Time: 1992 2011 (20 years) Surface boundary conditions: JRA-25 Viscous plastic dynamics [Hibler, 1979]

Regional Arctic solutionImportance of sea ice deformation for model mass balanceSea ice deformation fields in model and satellite observations #2Model Sensitivity to Ice Strength PmaxChange of sea ice strength parameter P* to simulate changes in ice deformation18 km grid spacing19922009 Ice strength3 experimentsBaseline P*: optimized Arctic solution (Nguyen et al., 2011; P*=2.3104) 0.7 P*: P* reduced by 30% (P* =1.6104) 0.3 P*: P* reduced by 70% (P* =0.7104)

Model DomainArcticBasinSensitivity Experiment: #Sea Ice Deformation RateDeformation rate As expected sea ice deformation (and speed) increases for lower ice strength

P*0.7 P*0.3 P*Seasonal Cycle Sea Ice Deformation Rate

Difference: experiment - baseline(0.7 P*) P*(0.3 P*) P* #4

Influence on Sea Ice VolumeTotal sea ice volume within the Arctic Basin is higher for weaker ice, i.e., higher deformation rates.

P*0.7 P*0.3 P*Arctic Basin Sea Ice Volume1992199519982001200420072010123x 104km3Difference to Baseline9294980004061020000400060008000(0.3 P*) P*(0.7 P*) P*km3960208 #5

Sea Ice Volume ExportHowever, the weaker ice experiments show an enhanced seasonal cycle and 0.3 P* a negative bias of 43 km3/month or ~20%.Ice Volume Export: Difference to baseline(0.7 P*) P*(0.3 P*) P*Arctic Basin Ice Volume ExportP*0.7 P*0.3 P*

Sea ice volume export out of the Arctic Basin(combined Fram Strait, CAA, Bering Strait, etc.) all three experiments are highly correlated #

Influence on Mixed Layer DepthThe winter mixed layer depth increases for higher deformation rates, i.e., lower ice strength.Also the variability of the mixed layer depth increases.P*0.7 P*0.3 P*Seasonal Cycle Mixed Layer Depth (92-09)Standard Deviation Mixed Layer DepthP*0.7 P*0.3 P* #7Conclusions Model Sea Ice Strength Sensitivity Sea strength and ice deformation processes strongly influence the sea ice mass balance in a coupled ocean-sea ice model using a viscous-plastic rheology.A new, higher equilibrium ice mass is establishedSea ice export shows stronger seasonal cycleReduced sea ice export for very low ice strength (probably caused by thicker ice)Deeper winter-time mixed layer depthChanges can be attributed to enhanced sea ice dynamicsSea ice deformation processes should be adequately represented in the model for realistic sea ice mass balance simulations next topic #8Comparison to RGPS Satellite Data

divergencevorticityshearmultiyear ice fraction20-23 Feb. 2005

RADARSAT Synthetic Aperture Radar (SAR) dataSpatial cross-correlation of patterns ice movement

1996 #9Calculate strain rates (divergence, vorticity, shear) from Lagrangian cells3-daily on 12.5 km grid

Example:November 1999

black line:perennial ice

RGPS and Model Sea Ice Deformation

Sea ice deformation parameters: divergence, vorticity and shearNumber and concentration of linear kinematic features (LKF) increase with decreasing model grid spacing. #10Difference in Deformation RateDeformation rate:RGPS data reconstructed from model outputRGPS D is by about 50% higherModel and observations highly correlated and show similar trends

#11Difference in Ice Deformation DistributionBiggest difference between RGPS and model in the seasonal ice zone suggests thin ice is too strong in modelChange of sea ice strength parameterization neededDifference distribution similar for all three model resolution

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#Way Forward: Material-Point Method

Deborah Sulsky, Han Tran, Kara PetersonUniversity New MexicoNew sea ice rheology: material-point methodSulsky et al. (2007), JGRCoupled to MITgcm ocean model #Last nights results

#ConclusionsDeformation of sea ice play an important role in viscous-plastic ice models. Small changes in the ice strength change the sea ice mass balance.Compared to RGPS observations, our three model solutions do not adequately reproduce small scale deformation and linear kinematic features (LKFs). Also the overall modeled deformation rate is about 50% lower than the observed one.Increase in model resolution produces a higher density and more localized ice deformation features.A new sea ice rheology might be necessary to reduce differences between modeled and observed ice kinematics. #16