Monthly extent climatologies are intended for users interested in persistence of ice over a particular month during the time series, October 1978 through December 1999. Individual ocean pixels containing a minimum of 15 percent ice cover are summed throughout the time series. Data are stored in two-byte integer format. For the Northern Hemisphere the grid size is 304 x 448 pixels, and the Southern Hemisphere grid size is 316 x 332 pixels. Land is set to a value of 200, coastlines to a value of 210, and lakes to a value of 220.
Data are in flat binary format, of two-byte integer type, scaled by ten.
Dates represent which years went into the averaging process. The first processing step involved averaging the sea ice concentrations for each series of months throughout the time series, November 1978 through December 1999, to create 12 monthly ice concentration climatologies for the entire series. Ocean mask files exist for each month of the time series. If ice was present in any of the twelve monthly ocean masks, the corresponding pixels were classified as ice in the final ice extent image. GIF images are also provided.