ATmo ch 8

Air Mass

A large body of air with similar temperature and humidity characteristics.

Source Regions

Regions of light winds and uniform topography where air masses form, such as the Arctic, oceans, or big flat land.

P

Polar air mass.

T

Tropical air mass.

A

Arctic air mass.

m

Maritime air mass (formed over water).

c

Continental air mass (formed over land).

cA (Continental Arctic)

Extremely cold, dry, and stable air mass originating over ice- and snow-covered surfaces.

cP (Continental Polar)

Cold, dry, and stable air mass that often forms in Canada.

cT (Continental Tropical)

Hot and dry air mass that is stable aloft but unstable near the surface; typically occurs in summer in the Southwest.

mP (Maritime Polar)

Cool, moist, and somewhat unstable air mass originating over the Pacific or Atlantic oceans.

mT (Maritime Tropical)

Warm, moist, and usually unstable air mass originating from the Gulf of Mexico, tropical Atlantic, or tropical Pacific.

Lake-Effect Snow

Snowstorms forming on the downwind (leeward) side of the Great Lakes when cold cP air moves over relatively warm water.

Pineapple Express

A flow of maritime tropical (mT) air from the tropical Pacific near Hawaii into California, often causing flooding.

Front

The boundary between two air masses, defined by temperature and humidity differences.

Cold Front

A "dome" of dense cold air replacing warm air, often featuring a steep leading edge and strong upward motion.

Warm Front

Warm air replacing cold air along a relatively gentle slope, leading to a broad area of upward motion.

Stationary Front

A front that does not move much; it can lead to flooding if moist air persists along the boundary for many days.

Occluded Front

A front that develops when a cold front catches up to and overtakes a warm front.

Cold Occlusion

A type of occluded front where the air behind the front is colder than the air it is overtaking.

Warm Occlusion

A type of occluded front where the air behind the front is milder (cool) than the very cold air ahead of it.

Synoptic Scale

The atmospheric scale that air masses and fronts typically fit into.

Dryline

A boundary separating hot, dry continental tropical (cT) air from warm, moist maritime tropical (mT) air, common in the southern Plains.

Pressure Trough

A "kink" in the isobars that may show a wind shift but has very little temperature gradient.

Cold Air Damming

A phenomenon where mountains (like the Appalachians) impede circulation, causing a shallow pool of cold air to be trapped at the surface