Sea-ice roughness

The sea-ice surface forms the boundary between ice and atmosphere. As such, its morphological properties influence the interactions between atmosphere and ice, or if snow is present, the interactions between the atmosphere and the snow cover. This is particularly true for the transfer of energy and momentum. The transfer of momentum between atmosphere and ice is substantially larger over a rough surface compared to a smooth surface. The properties of the sea-ice surface therefore influence the dynamical and thermal structure of the atmospheric boundary layer. To understand the transfer of momentum, an in-depth understanding of the surface roughness is required. To model the processes in the atmospheric boundary layer, it is therefore important to incorporate the roughness. The same holds for the ice underside, whose morphological properties influence the interactions between ice and ocean. With regards to modelling the dynamics of sea ice on both regional and global scales, an improved understanding of the sea-ice roughness and deformation processes is also desirable.

Knowledge of sea-ice roughness also has implications for estimating the mass balance of sea ice. Sea-ice deformation such as ridging and rafting are macroscopic processes, and the resulting deformation features are an important contribution to the total ice mass. These large-scale roughness features are also visible in satellite images of the sea-ice surface.

Within the sea-ice physics group, direct investigation of the sea-ice roughness is routinely carried out by means of a helicopter-borne laser altimeter, complemented by ground-truth measurements of snow thickness and pressure ridge heights. The surface roughness profiles obtained by laser altimetry allow detailed investigations of heights, spacings and the distributions of pressure ridges. In addition, as part of our remote-sensing activities, we investigate sea-ice roughness in satellite images. SAR signatures of deformed ice are analysed and compared to in-situ data in order to retrieve deformation parameters.

The picture shows examples of surface roughness profiles from different regions of the Arctic and Baltic. It illustrates the observed large regional differences in surface roughness. The height as seen by the laser represents the surface elevation relative to the level ice height.