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Arctic Outbreaks

© Keith C. Heidorn

Arctic Outbreaks. They happen in all months of the year and can rate headlines during spring, summer, or early autumn if they bring extreme drops in temperature or killing frost. But it is during the winter that they receive the most attention because arctic outbreaks can drop air temperatures to hazardous levels, increase demands for home heating fuels, produce lake/sea effect snows, or in their deepest southern penetration kill sensitive fruit and vegetable crops in the southern American states.

As we reach mid-winter, with the polar night having been well established for many months over the northern land masses within the Arctic Circle — Alaska, northern Canada, eastern Russia and Siberia — the continually-building cold almost defies description. Its depth can be best expressed by the Winnipeg, Manitoba settler who wrote in his diary one cold winter night in 1879: "Upon retiring for the night, I tried to blow out the candle, but the flame was frozen, so I had to break it off."

Meteorologists classify the frigid Northern Hemisphere air masses as Arctic when they are born north of the Arctic Circle and Continental Polar when they form in the subpolar Canadian North and Alaska. Both are typified by extremely cold temperatures and very little moisture with the Arctic flavour being of the super-sized variety.

Northern latitudes are the breeding grounds
for Arctic and Continental Polar air masses.

In the birth grounds of these air masses, the long, dark winter nights couple with clear skies and surfaces covered with snow and ice to continually chill the air. Since in these regions the sun does not rise, or only skirts the horizon for much of January, no warming heat from the sun alleviates the cold. The surface snow and ice reflect away most of what little sun weakly beams down. To accentuate the lack of incoming heat, snow very effectively radiates away what little heat it has, thus dropping surface air temperatures until they reach the temperature of the high atmosphere.

The air masses build for some time in these frigid cradles, and the more time they spend in their deep-freeze birthing grounds, the cold and drier they become, chilling the air to bitter temperatures, often less than minus 40 ^oC/F. As a result of that extreme cold, arctic air masses have an extremely low water vapour content (absolute humidity). The low water vapour content further permits the loss of heat from the surface and the air above it because water vapour is a very effective greenhouse gas. The lower the water content, the more radiative heat is lost directly to space.

The copyright of the article Arctic Outbreaks in Meteorology is owned by Keith C. Heidorn. Permission to republish Arctic Outbreaks in print or online must be granted by the author in writing.