For arctic service, it's a ribbon, and I believe it's 28 consecutive or non-consecutive days above the circle. My first deployment was to Kef, the ribbon was relatively new at that point, and the CO made it a point to have our flights above the circle specifically noted. Pretty much every flyer came away from the deployment with the ribbon.
When the Kef deployments were a regular thing, pretty much every aircrew got one because you were operating up there so much. I think it was 30 missions, or something. I remember one fly-by of an American sub who had breached the ice IVO the north pole and people were scampering around on the ice - that was kind of cool. 
