The Hibler ice model is formulated to include multi-year as well as first-year sea-ice concentrations. The multi-year ice coverage simulated by the model for the years 1978–85 is compared with corresponding satellite-derived coverage in the central Arctic and five sub-regions. The satellite data are obtained from the Nimbus-7 SMMR (Scanning Multifrequency Microwave Radiometer).

Changes of the regional multi-year coverage are compared on a monthly and seasonal basis for the non-summer seasons, and the model results are used to extend the microwave results to the melt season. The model-derived changes due to advection and convergence/divergence are distinguished from the melt-induced changes in order to assess the relative importance of model dynamics and thermodynamics to the normal seasonal cycle and the inter-annual variability of the simulated multi-year ice. Extreme deformation events that have produced long-lived signals in the microwave imagery are examined quantitatively by comparisons of model- and satellite-derived changes of multi-year coverage over synoptic time-scales. The model/satellite discrepancies on these shorter time-scales are diagnosed in terms of buoy measurements and the environmental parameters used to drive the model.