– are a continuous body of mixed gases that surrounds the planet, it is by no means a uniform blanket of air. It is composed of many large, variable parcels of air that are distinct from one
It must be large. A typical air mass is more than 1600 kilometers across and several kilometers deep.
It must have uniform properties in the horizontal dimension. This means that at any given altitude in the mass, its physical characteristics – primarily temperature, humidity, and stability
– are relatively homogeneous.
It must be a recognizable entity and travel as one. Thus, it must be distinct from the surrounding air, and when it moves, it must retain its original characteristics and not be torn apart by
differences in airflow.
North American Air Masses
– The lack of mountains trending east to west permits polar air to sweep southward and tropical air to flow northward unhindered by terrain, particularly over the
eastern two-thirds of the continent. The north-south mountains on the west coast impede the movement of the pacific air masses, causing significant modification of their characteristics.
Continental polar air masses
develop in central and northern Canada, and Arctic air masses originate farther north. These are similar except one is A is drier and colder. They are cold, dry, and stable.
Maritime Polar –
pacific mp brings widespread cloudiness and heavy precipitation to the mountainous coastal regions, but is severely modified when crossing the western ranges. Produces fog and
stratus clouds. Atlantic ap does not affect North America because the prevailing circulation of the atmosphere is westerly.
is warm, moist, and unstable from the Caribbean and gulf of Mexico strongly influences the weather east of the rockies and bring uncomfortable amounts of heat. Pacific mt air
originates over water in areas of anticyclonic subsidence, and so it is cooler, drier, and more stable than Atlantic mt air. In winter the air produces some coastal fog and rainfall if forced up the
mountain slopes and produces summer rains.
air is relatively unimportant in North America because its source region is not extensive and consists of varied terrain. In summer hot, very dry, unstable ct air develops. It rushes
into the great plains bringing heat waves and drought.
air affects North America only in association with hurricanes. Similar to Mountain air except E air provides more rain than mountainair because of higher humidity and instability.
when unlike air masses meet, they do not mix readily; instead, a boundary zone called a front develops between them. It consists of a relatively narrow but nevertheless three-dimensional
zone of discontinuity within which the properties of the air change rapidly. They are several kilometers wide. The concept was developed during WWI by a Norwegian.
It was like troops clashing
against one another at the battlefront. Front lean upward from the surface, the slope of the front allows the air to be uplifted and adiabatic cooling to take place. Front lean so much that they are more