Feb 13, 2007 - Yesterday saw the effects of yet another Arctic Air Mass in New England.
What is the difference between "polar air" and "arctic air" ?
Polar air masses are cool or cold and dry, but not as cold as an arctic air mass which is extremely cold, contains very little moisture and forms at or near the Arctic Circle.
Arctic air masses form primarily the winter over the Arctic Basin, Greenland, and the northern interior of North America.
Despite the difference by definition in temperature, "arctic air is cold aloft and extends to great heights, but the surface temperatures are often higher than those of polar air.." (AMS Glossary - arctic air)
Definition of an Air Mass from: NWS Billings Montata Office - Weather Talk - Air Masses and Fronts
"Air masses are basically large weather systems with homogeneous temperature and moisture characteristics that are created and classified by the geography where they formed. If an airmass originates over water, it is called a maritime airmass. If it forms over land, it is called a continental airmass. These two airmass types are moisture-dependent, so if an airmass is a maritime one, it tends to be humid, while a continental one tends to be dry.
Airmass type also depends on how much sunlight the ground under it receives in a given location over a period of time. Air masses closer to the tropics get more sunshine, and are thus warmer than air to the north. Such air masses are referred to as tropical, while air masses which form closer to the poles are colder, and are called polar. An airmass which forms over the arctic ice cap near the pole itself is termed an arctic airmass. Using these broad groups of airmass types, meteorologists are able to classify any airmass, in general terms, across the entire planet."
Air Masses are described in nice detail with graphics at the Meteorological Service of Canada - Air Masses:
FORMATION AND CLASSIFICATION OF AIR MASSES
- Continental arctic
- Continental polar
- Continental tropical
- Maritime arctic (primarily Canadian)
- Maritime polar
- Maritime tropical
FACTORS THAT DETERMINE WEATHER WITHIN AN AIR MASS
CHANGES IN AIR MASSES
WEATHER ASSSOCIATED WITH AIR MASSES
Another illustrated site which explains air masses and surface charts can be found at TAMU
Air Masses and Surface Charts
And from the Archives, the United States Department of Agriculture, Weather Bureau, Monthly Weather Review.. This 1940 document includes a section on the formation of continental arctic air.
"FORMATION OF CONTINENTAL ARCTIC AIR"
"It has been shown by Wexler3 that the formation of continental Arctic air masses * comes about mainly as the result of cooling of the lower atmosphere by radiation processes over the northern snow-covered continents and ice fields during the winter night. If these areas represent a true cold source, then air masses reaching there from other localities must always be at higher temperatures at first, then become Arctic in character through cooling. Since a migration of air masses from one part of the earth to another is occurring constantly, the building up of continental Arctic air from previously warmer air masses, their outbreak into lower latitudes after having achieved the low temperatures, and their replacment by new air masses which are relatively warm in the beginning but undergo the same cooling to form again more Arctic air, are continuous processes."
Read the FULL ARTICLE HERE source: NOAA Repository.