Gridded Monthly Sea Ice Extent and Concentration, 1850 Onward, Version 1

Observations from historical sources are the basis of this monthly gridded sea ice concentration product that begins in 1850. In 1979, these sources give way to a single source: concentration from satellite passive microwave data. The historical observations come in many forms: ship observations, compilations by naval oceanographers, analyses by national ice services, and others. Monthly sea ice concentration is given in a 1/4 degree latitude by 1/4 degree longitude grid. In addition to the concentration array, for each month a corresponding source array indicates where each of 16 possible sources is used.The file of concentration and source arrays conforms to NetCDF-4 standards.