Counter defines time period of observations upon which chart is based (i.e. 1972, Jan 03). Use buttons [>>] and [<<] to browse forward and backward in time. Use [Step]-menu to choose between weekly, monthly and yearly step during browsing. Use button [2x1] to switch to dual window mode to compare pairs of charts. Use [Scroll] checkbox to (dis)enable autoscrolling. Use [time] checkbox to switch scrolling forward and backward in time. Use buttond [+] and [-] to accelarate or slow down autoscrolling.
Given array is based on processing weekly USA National Ice Center (NIC) sea ice conditions charts prepared in World Meteorological Organization SIGRID format (WMO, 1989) for 1972-1994 interval separately for Arctic East (90W eastward to 90E; 45N to 90N) and Arctic West (90E eastward to 90W; 45N to 90N). Layer of sea ice total concentration is depicted in polar stereographical projection.