Midlatitude Cyclones Exercises 22 and 23

Air Masses• Atmosphere is made up of large air masses

• Large - 1000 miles across, several kilometers deep • Uniform properties of temperature, humidity and

stability • Travel as one and distinct from surrounding air

• Can form anywhere • Causes distinct properties

North American Air Masses

Fronts

• Boundary zone between unlike air masses • Narrow zone where air properties change rapidly • Normally defined by a difference in temperature • Can be stationary but more likely constantly in

motion • Four types of fronts – Warm – Cold – Stationary – Occluded

• Warm front • Brings warm air into an area • Clouds and precipitation • Gentle transition • No convective activity

• Cold Fronts • Brings cold air by displacing warm air mass • Rapid lifting of warm air • Unstable, violent weather • Thunderstorms, convection cells

Midlatitude cyclones• Most significant of all atmospheric disturbances • Large migratory low pressure systems • Move with the westerlies • Responsible most precipitation • Oval shaped, about 1000 miles in diameter

• Low pressure system • Counterclockwise rotation • Cool air from the north • Warm air from the south • Precipitation along both fronts

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