Proportion of time the ocean is covered by sea ice of concentration 85% or higher. Calculated from AMSR-E satellite estimates of daily sea ice concentration at 6.25 km resolution, using concentration data from 1-Jul-2002 to 30-Jun-2011. The fraction of time each pixel was covered by sea ice of at least 85% concentration was calculated for each pixel in the original (polar stereographic) grid. Reference: Spreen G, Kaleschke L, Heygster G (2008), Sea ice remote sensing using AMSR-E 89 GHz channels, J. Geophys. Res., doi:10.1029/2005JC003384 http://www.ifm.zmaw.de/en/research/remote-sensing-assimilation/sea-ice/amsr-e-sea-ice-concentration/ Editor Sea Ice Takeshi Tamura tamura.takeshi@nipr.ac.jp