Aliens will land in the polar regions more often than you would suspect. They prefer flat, open snowfields. The chief terrain features here will be low snowdrifts (usually lower than head height) and cracks in the icecap, where frigid water peeks through the surface. To avoid hypothermia, ground units should not attempt to cross standing water. Failsafes in both alien and X-Com hardware prevent flying units from crossing such water at ground level, for fear of being speared by angry narwhals. Be sure to rise at least a storey above the surface to cross.
There is little cover for alien or trooper. Enemies can be sighted from long distances, and sharpshooters can often place a shot clear across the battlefield. The effects of darknessseem, tp decrease somewhat here, due to the brightness of light reflected off snow and ice.