This chapter presents the geophysical background of mesoscale to large-scale sea ice modelling, discusses the structure of existing advanced models, and shows results from model simulations on future sea ice conditions in the Arctic Ocean. The first and second section introduce the theory of material description of sea ice, sea ice thermodynamics, and the fundamental equations of sea ice dynamics -conservation laws of ice, momentum and heat, and sea ice rheology. Thermodynamics is a one-dimensional problem while dynamics when integrated across sea ice thickness becomes a twodimensional problem, and they are linked together by the ice conservation law. Forcing of sea ice dynamics and thermodynamics is via atmospheric and oceanic boundary layers, where parameterizations of exchange of momentum, heat, moisture, and salinity are of key importance.Sea ice properties relevant to climate are primarily sea ice extent, concentration and thickness.Mesoscale and large-scale sea ice models treat sea ice as a continuum by thickness distribution. These models consist of momentum equation, conservation laws of heat, salt and ice, and ice rheology. The main models used for climate investigations are the Los Alamos model CICE (Community Ice CodE) and LIM (The Louvain-la-Neuve Sea Ice Model), which are reviewed including their parameterizations.Moreover, the performance of these two main models are briefly assessed against observational reference data based on hindcasts and projections. Aspects of data assimilation are discussed where modelling is closely linked to sea ice remote sensing data. Specific attention is given to model performance in sea ice simulation using runs from CMIP3 (Coupled Model Intercomparison Project, Phase 3) and CMIP5 (Coupled Model Intercomparison Project, Phase 5). Sea ice extent and thickness are considered as the most important climate variables, which are needed for validation of current climate models. To validate model performance, comprehensive data sets are also required. Several important characteristics were considered and compared with observations: sea ice cover for seasons with maximum and minimum sea ice extent, sea ice trend in September, sea ice annual cycle, linear trend of sea ice area and volume, sea ice thickness distribution. A brief review is also provided for sea ice assimilation system and its current performance capability.
8.1Sea ice geophysics
Sea ice fieldsA "sea ice landscape" consists of leads and ice floes with ridges, hummocks and other morphological characteristics. Mechanical behavior of sea ice fields depends largely on ice concentration, the relative It is common in the seasonal sea ice zone where snow accumulation is large. There are two more specific forms of ice: anchor ice and platelet ice. Anchor ice forms in the sea bottom in turbulent conditions in shallow regions, and it may rise to surface with bottom sediments due to its buoyancy. This is observed, e.g., in the Siberian shelf. Platelet ice forms in Antarctic waters next to floating ice shelves, which act as...