An air mass that has its source region over the Arctic or Antarctic regions. In winter, when there is largely unbroken ice cover across the Arctic Ocean, it initially has continental characteristics (cA), but is rapidly modified on crossing open water, being warmed from beneath, and thus becoming unstable. It is generally similar to maritime polar air, but colder throughout its depth. In summer, it originates directly over the open pack ice in both the Arctic and Antarctic, and there are additional sources at high latitudes over Canada and Eurasia (particularly Siberia), where the extensive marshy ground means that the regions more closely resemble maritime than continental areas, and affect the air mass accordingly. See Arctic air.
Subjects: Meteorology and Climatology.