Microwave signatures of first-year and multiyear sea ice

The deformation of a strain triangle (≈6 km × 8 km × 11 km) located on first-year ice in the Beaufort Sea was observed over a two-week period in March 1971. Significant strain events (≈ 1.5%) were observed to occur during short (≈6 h) time periods. The long-term (one day or more) divergence rate varied between 0.04 and 0.08 × 10 −3 h −1 . Short-term divergence rates showed values as high as 0.29 × 10 −3 h −1 . The observed shearing motion indicated that the floes to the east were moving to the south relative to the floes to the west. This agrees with the shear pattern that might be expected considering the location of the station in the Pacific Gyre. Studies of fracture (lead and crack) orientations in the vicinity of the strain triangle indicate reasonable correlations with the orientation of the strain-rate ellipse. A qualitative relation is suggested between the fracture density and the long-term divergence rate. Correlations were also observed between the divergence of the wind field as computed from the surface pressure field and the ice divergence.