Objectives

1. Compare and contrast the three major wind systems. Identify four types of fronts. Distinguish between high- and low-pressure systems. Section 12.2 Objectives Weather Systems

2. Weather results when air masses with different pressures and temperatures move, change, and collide. Section 12.2 Weather Systems Review Vocabulary convection: the transfer of thermal energy by the flow of a heated substance

3. Section 12.2 Weather Systems New Vocabulary Coriolis effect polar easterlies prevailing westerlies trade winds jet stream front

4. The directions of Earth’s winds are influenced by Earth’s rotation. This Coriolis effect results in fluids and objects moving in an apparent curved path rather than a straight line. Section 12.2 Global Wind Systems Weather Systems

5. Section 12.2 Global Wind Systems Weather Systems The directions of Earth’s wind systems, such as the polar easterlies and the trade winds, vary with the latitudes in which they occur.

7. Section 12.2 Global Wind Systems- 3 systems Weather Systems 1.Polar easterlies The polar easterlies are the wind zones between 60 N latitude and the north pole, and 60 S latitude and the south pole.

8. Section 12.2 Global Wind Systems Weather Systems 2.Prevailing westerlies The prevailing westerlies are the wind systems on Earth located between latitudes 30 N and 60 N, and 30 S and 60 S.

9. Section 12.2 Global Wind Systems Weather Systems 3.Trade winds Between latitudes 30 N and the equator is a circulation belt of wind known as the trade winds.

10. Section 12.2 Global Wind Systems Weather Systems Trade winds Near latitudes 30 N the sinking air creates an area of high pressure. This results in a belt of weak surface winds called the horse latitudes.

11. Section 12.2 Global Wind Systems Weather Systems Trade winds Trade winds from the North and the South meet and join near the equator.The air is forced upward, which creates an area of low pressure called the intertropical convergence zone (ITCZ).

12. Section 12.2 Jet Streams Weather Systems A large temperature gradient in upper-level air combined with the Coriolis effect results in strong westerly winds called jet streams. A jet stream is a narrow band of fast, high-altitude, westerly wind.

13. Section 12.2 Jet Streams Weather Systems Weather in the middle latitudes ( our area)is strongly influenced by fast-moving, high-altitude jet streams.

14. Section 12.2 Jet Streams Weather Systems Two Types of jet streams The major jet streams, called the 1.polar jet streams, separate the polar easterlies from the prevailing westerlies. The minor jet streams are the 2.subtropical jet streams. They occur where the trade winds meet the prevailing westerlies.

15. Section 12.2 Jet Streams Weather Systems Jet streams and weather systems Storms form along jet streams and can generate large-scale weather systems. Jet streams affect the intensity of weather systems by moving air of different temperatures from one region of Earth to another.

16. Section 12.2 Fronts- 4 types Weather Systems A collision of two air masses forms a front—a narrow region between two air masses of different densities.

18. Section 12.2 Fronts Weather Systems 1.Cold front When cold, dense air displaces warm air, it forces the warm air, which is less dense, up along a steep slope. This type of collision is called a cold front. Intense precipitation and sometimes thunderstorms.

19. Section 12.2 Fronts Weather Systems 2.Warm front Advancing warm air displaces cold air along a warm front. A warm front develops a gradual boundary slope. Widespread light precipitation

20. Section 12.2 Fronts Weather Systems 3.Stationary front When two air masses meet but neither advances, the boundary between them stalls. This stationary front frequently occurs between two modified air masses that have small temperature and pressure gradients between them. Sometimes light winds and precipitation

21. Section 12.2 Fronts Weather Systems 4.Occluded front Sometimes, a cold air mass moves so rapidly that it overtakes a warm front and forces the warm air upward. As the warm air is lifted, the advancing cold air mass collides with the cold air mass in front of the warm front.A warm air mass is squeezed upward between two cold air masses Strong winds and heavy precipitation

22. Section 12.2 Pressure Systems Weather Systems Sinking or rising air, combined with the Coriolis effect, results in the formation of rotating high- and low-pressure systems in the atmosphere.

23. Section 12.2 Pressure Systems – 2 types Weather Systems 1.Low-pressure systems In surface low-pressure systems, air rises. When air from outside the system replaces the rising air, this air spirals inward toward the center and then upward. Clouds and precipitation

24. Section 12.2 Pressure Systems Weather Systems 2.High-pressure systems In a surface high-pressure system, sinking air moves away from the system’s center when it reaches Earth’s surface. Clear skies and fair weather.

25. Section 12.2 Pressure Systems Weather Systems In the northern hemisphere, winds move counterclockwise around a low-pressure center, and clockwise around a high-pressure center. Low-pressure center High-pressure center

26. 12 Section 12.2 Weather Systems Study Guide Key Concepts Weather results when air masses with different pressures and temperatures move, change, and collide. • The three major wind systems are the polar easterlies, the prevailing westerlies, and the trade winds.

27. 12 Section 12.2 Weather Systems Study Guide Key Concepts • Fast-moving, high-altitude jet streams greatly influence weather in the middle latitudes. • The four types of fronts are cold fronts, warm fronts, occluded fronts, and stationary fronts. • Air moves in a generally circular motion around either a high- or low-pressure center.

28. 12 12.2 Section Questions Meteorology Along which type of weather front does one cold front overtake another cold front? a.cold front b.warm front c.stationary front d.occluded front

29. 12 12.2 Section Questions Meteorology Which description characterizes a low-pressure center in the northern hemisphere? a.Air spirals out and rises. b.Air spirals in and rises. c.Air spirals out and sinks. d.Air spirals in and sinks.

30. 12 12.2 Section Questions Meteorology At which latitudes are the horse latitudes? a.at about 10 N and 10 S b.at about 30 N and 30 S c.at about 60 N and 60 S d.at about 80 N and 80 S