Compressive ice is considered to be amongst the worst operating conditions when navigating in ice and demanding for icebreaker assistance. Compression is a manifestation of ice cover stresses and a phenomenon physically different from convergence. Indeed, severe compression is often experienced in an inert ice cover and is reduced by the onset on convergence. This paper presents investigations to reach better understanding of processes generating ice compression by analyzing model forecasting methods and direct field observations.

Producing relevant information on compressive conditions to shipping and ice management by enhancing numerical ice forecast modelling. Products comprise specific areal characterization, pressure along channels or routes and in the vicinity of critical areas.

Predictability of compression in sea ice by numerical modelling encounters considerable challenges. Local stresses can be forecasted from deterministic model results, but these do not easily capture the rapidly fluctuating nature of the stress propagation. This has been concluded through extensive in-situ stress measurements, drift buoy measurements and ship observations and comparisons to numerical sea ice model results.

To be able to serve shipping in ice with sensible information, study results support an ensemble forecasting approach and provide probabilistic ice pressure products. The ensemble averaged mean compression fields in such a forecast appears reliable and is easily adoptable by the end users. This kind of a forecasting approach is completely new and has (to authors' knowledge) not been carried out for this purpose before. Systematic studies of compression, involving the whole chain from ice cover dynamics to the ship experiences, have been lacking.

Ice pressure has in some applications been claimed to be obtained from satellite image analysis. One should be cautious with such interpretations, since even if there is an obvious coupling between converging (or compacting) ice and pressure, they represent different physical phenomena. This has also been noted in the most recent updates of WMO definitions of ice features, making a distinction between these two features.

A comprehensive approach has been made to forecast ice pressure, an issue which until now seems to have been avoided by the ice modelling community due to its complex nature. Inclusion of compression in real-time operative ice forecasts in an adaptable form substantially improves decision making.

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