1. Sea Ice Deformation Studies and Model Development
Gunnar Spreen, Han Tran, Ron Kwok, and Dimitris Menemenlis

2. Importance of sea ice deformation for model mass balance
Overview
Importance of sea ice deformation for model mass balance
Sea ice deformation fields in model and satellite observations
Regional 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 solution

3. Model Sensitivity to Ice Strength Pmax
Change of sea ice strength parameter P* to simulate changes in ice deformation
18 km grid spacing
1992–2009
Ice strength
3 experiments
Baseline P*: optimized Arctic solution (Nguyen et al., 2011; P*=2.3·104)
0.7 P*: P* reduced by 30% (P* =1.6·104)
0.3 P*: P* reduced by 70% (P* =0.7·104)
Sensitivity Experiment:
Model Domain
Arctic
Basin

4. Sea Ice Deformation RateP*
0.7 P*
0.3 P*
Seasonal Cycle Sea Ice Deformation Rate
Difference: experiment - baseline
(0.7 P*) – P* (0.3 P*) – P*
Deformation rate
As expected sea ice deformation (and speed) increases for lower ice strength

5. Influence on Sea Ice VolumeP*
0.7 P*
0.3 P*
Arctic Basin Sea Ice Volume
1992
1995
1998
2001
2004
2007
2010 1 2 3
x 104
km3
Difference to Baseline
km3
(0.7 P*) – P*
8000
(0.3 P*) – P*
6000
4000
2000 92 94 96 98 00 02 04 06 08 10
Total sea ice volume within the Arctic Basin is higher for weaker ice, i.e., higher deformation rates.

6. Arctic Basin Ice Volume Export
Sea Ice Volume Export
Arctic Basin Ice Volume Export
Sea ice volume export out of the Arctic Basin (combined Fram Strait, CAA, Bering Strait, etc.)
all three experiments are highly correlated
Ice Volume Export: Difference to baseline
(0.7 P*) – P* (0.3 P*) – P* P*
0.7 P* 0.3 P*
However, the weaker ice experiments show an enhanced seasonal cycle and “0.3 P*” a negative bias of 43 km3/month or ~20%.

7. Influence on Mixed Layer Depth
Seasonal Cycle Mixed Layer Depth (92-09)
Standard Deviation Mixed Layer Depth P*
0.7 P*
0.3 P* P*
0.7 P*
0.3 P*
The winter mixed layer depth increases for higher deformation rates, i.e., lower ice strength.
Also the variability of the mixed layer depth increases.

8. Conclusions 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 established
Sea ice export shows stronger seasonal cycle
Reduced sea ice export for very low ice strength (probably caused by thicker ice)
Deeper winter-time mixed layer depth
Changes can be attributed to enhanced sea ice dynamics
Sea ice deformation processes should be adequately represented in the model for realistic sea ice mass balance simulations → next topic

9. Comparison to RGPS Satellite Data
RADARSAT Synthetic Aperture Radar (SAR) data
Spatial cross-correlation of patterns → ice movement
divergence
vorticity
shear
multiyear ice fraction
20-23 Feb. 2005
1996
Calculate strain rates (divergence, vorticity, shear) from Lagrangian cells
3-daily on 12.5 km grid

10. RGPS and Model Sea Ice Deformation
Example: November 1999
black line: perennial ice
Sea ice deformation parameters: divergence, vorticity and shear
Number and concentration of linear kinematic features (LKF) increase with decreasing model grid spacing.

11. Difference in Deformation Rate
RGPS data reconstructed from model output
RGPS D is by about 50% higher
Model and observations highly correlated and show similar trends

12. Difference in Ice Deformation Distribution
Biggest difference between RGPS and model in the seasonal ice zone  suggests thin ice is too strong in model
Change of sea ice strength parameterization needed
Difference distribution similar for all three model resolution

14. Way Forward: Material-Point Method
Deborah Sulsky, Han Tran, Kara Peterson University New Mexico
New sea ice rheology: material-point method
Sulsky et al. (2007), JGR
Coupled to MITgcm ocean model

15. Last night’s results 

16. Conclusions
Deformation 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.