UNIT THREE: Matter, Energy, and Earth

2. UNIT THREE: Matter, Energy, and Earth • Chapter 8 Matter and Temperature • Chapter 9 Heat • Chapter 10 Properties of Matter • Chapter 11 Earth’s Atmosphere and Weather

4. Chapter Eleven: Earth’s Atmosphereand Weather • 11.1 Earth’s Atmosphere • 11.2 Weather Variables • 11.3 Weather Patterns

5. 11.3 Learning Goals • Define front. • Contrast warm and cold fronts. • Discuss the weather conditions associated with high-pressure and low-pressure systems. • Describe the characteristics of clouds and predict the weather based on the appearance of clouds.

6. An air mass is a large body of air with consistent temperature and moisture characteristics throughout. Two air masses that affect the United States are the continental polar air mass and the maritime tropical air mass. 11.3 Air masses and fronts Changing conditions and global winds cause these air masses to move.

7. 11.3 Fronts • A cold front occurs when cold air moves in and replaces warm air.

8. 11.3 Fronts • A warm front occurs when warm air moves in and replaces cold air.

9. On a weather map, a cold front is shown using a line marked with triangles. The triangles point in the direction the front is moving. A warm front is shown using a line marked with semicircles. 11.3 Fronts

10. 11.3 Low- and high-pressure areas • When a cold front moves into a region and warm air is forced upward, an area of low pressure is created near Earth’s surface at the boundary between the two air masses. • A center of high pressure tends to be found where a stable cold air mass has settled in a region.

12. 11.3 Clouds • A cloud is a group of water droplets or ice crystals that you can see in the atmosphere.

13. 11.3 Types of clouds • Different conditions cause different clouds. • Cumuliform clouds include: • cirrocumulus • altocumulus • cumulus • cumulonimbus

14. 11.3 Cloud formation • Stratiform clouds form when a large mass of stable air gradually rises, expands, and cools. • Stratiform clouds include: • cirrostratus • altostratus • stratus • nimbostratus

15. 11.3 Cloud formation • Sometimes a cloud formation combines aspects of both cumuliform and stratiform clouds. • We call these clouds stratocumulus clouds.

16. 11.3 Cloud formation • Cirrus clouds are thin lines of ice crystals high in the sky, above 6,000 meters. • They are just a thin streak of white across a blue sky.

17. Thunderstorms occur because of convection in the atmosphere. The downdraft and updraft form a type of convection cell called a storm cell within the cloud. 11.3 Thunderstorms

18. Lightning is a bright spark of light that occurs within a storm cloud, between a cloud and Earth’s surface, or between two storm clouds. It occurs when a spark travels between negative and positive charges. 11.3 Lightning

19. A hurricane is a tropical cyclone with wind speeds of at least 74 miles (119 km) per hour. The Saffir-Simpson Hurricane Scale is one scale used for rating hurricanes. 11.3 Hurricanes

20. A tornado, like a hurricane, is a system of rotating winds around a low-pressure center. As the rotating wind pattern narrows and lengthens, it forms a funnel cloud. 11.3 Tornadoes

21. 11.3 Funnel clouds • When updrafts in a storm cell reach high speed, they begin to rotate. • As th diameter of the rotation narrows and extends downward, a funnel cloud takes shape.

22. Investigation 11C Storms • Key Question: How does Doppler radar work?

23. Hurricane Hunters • Why would anyone intentionally fly into the driving rain and fierce winds of a hurricane? Hurricane hunters know their work saves lives and tax dollars.