Large temporary rigid areas in the Arctic sea ice cover form and disintegrate in a few days during winter. When these rigid areas are shore-fast, they eliminate moment flux from air to water via wind forcing on the ice. Temporary shore-fast ice causes mixing of upper stratified waters below the ice in areas of strong tidal currents. Satellite data and observations by explorers in the Arctic show that large rigid areas tend to break up during the summer. We can conclude that formation and breakup of rigid areas are sensitive to temperature. The present study illustrates techniques for satellite observation of the dynamics of the Arctic sea ice cover during winter. Better understanding of the physical mechanisms involved will enhance codes for such satellite observations. The study indicates anomalous/critical dynamics and scale invariance in the formation and breakup of rigid areas. These indications come from direct satellite observations and are supported by generic conceptual models for ice dynamics during winter. Critical phenomena often form fractal structures with no natural lengths. ¿ 1998 American Geophysical Union