GeoNotes - Air masses are a continuous body of mixed gases...

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Air masses – 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 another. Characteristics – 1. It must be large. A typical air mass is more than 1600 kilometers across and several kilometers deep. 2. 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. 3. 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. Maritime Tropical 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. Continental Tropical 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. Equatorial
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