Counter defines time period of observations upon which chart is based (e.g. 1972, Feb 11-20). Use buttons [>>] and [<<] to browse forward and backward in time. Use [Step]-menu to choose between weekly, monthly, yearly or decadal step during browsing. Given array is based on processing 10-days period Arctic and Antarctic Research Institute (AARI) sea ice conditions charts (left window) and weekly USA National Ice Center (NIC) sea ice conditions charts (right window), prepared in World Meteorological Organization SIGRID format (WMO, 1989). Layer of sea ice total concentration is depicted in EASE-grid polar stereographical projection.