A Climatology of Surface Albedo for the Antarctic Sea Ice Zone

During three springtime voyages of the Australian National Antarctic Research Expeditions (ANARE) in the East Antarctic sea-ice zone, spectral albedo was measured at wavelengths from 320 to 1060 nm for grease ice, nilas, young grey ice, young grey-white ice, bare first-year ice, snow-covered first-year ice, and open water. Albedos for spectral bands commonly used in GCMs, as well as the broadband solar albedo, were obtained by integrating the spectral albedos over wavelength, weighted by the solar spectrum. For combinations of ice and snow thickness that were not measured, an interpolation method was applied to determine the band albedos, resulting in a table of albedos for six ice types, each under three snow-cover conditions (thick snow, thin snow, or no snow) and for either clear or cloudy sky. These albedos can then be assigned to ice types reported in visual observations that use the standard protocol of the ASPECT (Antarctic Sea Ice Processes and Climate) project.

The ASPECT data set includes over 15,000 observations of sea ice type, thickness, concentration, and snow thickness in the ocean surrounding Antarctica, in all seasons, from ships of several nations. The observations were usually made hourly while the ship was underway; they give the fractional coverage of up to three types of ice in the region within one kilometer of the ship. The area-averaged albedo, for the ice-covered area within the field of view, is computed for each observation. The observations are binned into four seasons, four longitudinal sectors, and latitudinal zones of width 2.5 degrees. These ice-only albedos are then combined with the climatological ice concentrations for each region from 13 years of satellite passive microwave observations (SSM/I, bootstrap algorithm, 1988-2000).

The predominant factor determining the albedo in the sea ice zone is the area covered by open water.