Air Masses and Fronts

1. Air Masses and Fronts

2. Moving Air • Differences in air pressure are caused by unequal heating of the Earth’s surface with equatorial air receiving more heat and rising (causing low pressure) while the polar regions have sinking cold air (causing high pressure)

3. How Air Moves: • From high pressure to low pressure (thus from poles to equator) • Temperature differences create three wind belts per hemisphere • The Coriolis Effect caused by the rotation of the Earth influences air patterns

4. Air Mass: • Large body of air throughout which temperature and moisture content are similar • Created by: a stationary body of air that takes on the characteristics of that region

5. Air Masses: • Classified according to their source region: • Polar – forms in cold regions • Tropical – forms in warm regions • Continental – forms over land and thus dry • Maritime – forms over water and thus wet

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8. Fronts: • Boundaries between air masses; dense cold air does not mix with less dense warm air; do not exist in tropics because no real temperature differences

9. Cold Front: • The front edge of a moving mass of cold air that pushes beneath a warm air mass like a wedge; results in precipitation if warm air mass is humid, severe storms if cold front moves quickly

10. Warm Front: • The front edge of advancing warm air mass that replaces cold air with warmer air; generally result in precipitation over a large area

11. Stationary Front: • A front of air masses that move either very slowly or not at all, weather similar to warm front

12. Occluded Front: • A front that forms when a cold air mass overtakes a warm air mass and lifts the warm air mass off the ground and over another air mass