Air Masses
Learning Objectives
Air Mass: a body of air that retains its properties (temperature and moisture) over 1000's of kilometers. Characteristics are derived from the land surface over which the air mass sits. Pressure differences in the atmosphere causes the air mass to move, often into an area with an air mass that has different temperature and moisture content.
Air masses are defined by the area from which they come:
T Tropical
P Polar
A Arctic
m maritime
c continental
Hence an air mass with designation: mT originates from a tropical ocean region.
Continental Polar: originates from the interior of Canada and Alaska. Cold and dry.
Maritime Polar: originates in the ocean regions near the poles. Cold (not as cold as a cP air mass) and moist.
Maritime Tropical: originates from tropical ocean regions. Warm and moist
Continental Tropical: originate from inland tropical areas. Warm and dry.
Arctic: bitterly cold air moving from the Arctic.
Front: the transition zone between two air masses.
Cold Front: the air mass moving into an area is colder than the air that sits over that area.
Depicted as a blue line with diamonds that point in the direction of frontal movement.
Associated Weather: can have severe thunderstorms, severity dependent on the temperature difference on either side of the front.
Warm Front: the air mass moving into an area is warmer than the air that sits over that area.
Depicted as a red line with semi-circles pointing in the direction of frontal movement.
Associated Weather: cloudy and rainy, usually not severe.
Stationary Front: neither the cold air mass nor the warm air mass is moving.
Depicted as alternating red semicircles and blue diamonds pointing in opposite directions.
Occluded Front: forms when a cold front overtakes a warm front. Usually associated with mid-latitude cyclones.
