How Does Air Mass Influence Climate?

Air Masses

• Air masses represent large bodies of air that have a uniform set of characteristics, primarily temperature and moisture content. They form over source regions that enable them to slowly stabilize. As they move, they affect the climates of areas in their path, according to their unique characteristics. The five types of air masses that affect the climate in the U.S. are continental arctic, continental polar, maritime polar, continental tropical and maritime tropical.

Continental Arctic Air Masses

• Continental arctic air masses form over the planet's poles. They're characterized by extremely cold temperatures and relatively dry air. They typically only form during the winter months, as the sun warms the arctic too much during the summer. During winter, they move southward into the U.S., bringing extremely cold conditions to the northern states.

Continental Polar Air Masses

• Continental polar air masses form over large land masses, such as Canada, at latitudes greater than 60 degrees. They're characterized by cold temperatures and relatively dry air. They typically move southward into the U.S., east of the Rockies. This creates a continental climate for the northern states that features cool to warm summers and cold snowy winters.

Maritime Polar Air Masses

• Maritime polar air masses form over the North Pacific and North Atlantic oceans. They're characterized by cool temperatures and moist air and are responsible for the unique marine climate experienced in the Pacific Northwest. This climate features mild temperatures and frequent rainfall throughout the year. They also pump moisture into the Northeast, creating high snowfall during the winter months.

Continental Tropical Air Masses

• Continental tropical air masses form over Mexico and the southwestern U.S. They're characterized by very hot temperatures and very dry air. They create a desert climate in the Southwest that features hot days, large temperature fluctuations between day and night, and less than 10 inches of rainfall per year. They also contribute to the semiarid climate found in the plains of the Midwest.

Maritime Tropical Air Masses

• Maritime tropical air masses form over water in latitudes of less than 25 degrees, such as the Pacific, Atlantic and Gulf of Mexico. They're characterized by warm temperatures and very moist air. These air masses create a Mediterranean climate along the southwest coast of the U.S. They're also responsible for the humid subtropical climate found in the Southeast, featuring hot, humid summers and mild winters.