Weather Patterns 16.1 The atmosphere's air pressure changes. 16.2 CHAPTER NEW CHAPTER Weather Patterns the BIG idea Some features of weather have predictable patterns. 16.1 The atmosphere's air pressure changes. 16.2 The atmosphere has wind patterns. 16.3 Most clouds form as air rises and cools. 16.4 Water falls to Earth’s surface as precipitation. CHAPTER OUTLINE CHAPTER RESOURCES

The atmosphere's air pressure changes. 16.1 The atmosphere's air pressure changes. Air pressure is the force of air molecules pushing on an area. Air pressure and density as you move in the atmosphere. Air pressure can also differ in two locations at the same altitude (ex. pop cans). air pressure barometer CHAPTER RESOURCES SECTION OUTLINE

The atmosphere has wind patterns. 16.2 The atmosphere has wind patterns. Wind blows from areas of high pressure toward areas of low pressure. Earth's rotation causes long distance winds to curve. weather wind global wind Coriolis effect jet stream area of high pressure area of low pressure monsoon VISUALIZATION View an animation of the Coriolis effect. CLASSZONE.COM Explore how breezes blowing over land and water change over the course of a day. CHAPTER RESOURCES SECTION OUTLINE

Most clouds form as air rises and cools. 16.3 Most clouds form as air rises and cools. Clouds form when the air cools to it’s dew point and are made of tiny water droplets that condense from water vapor in rising air. evaporation condensation level where condensation begins precipitation humidity saturation relative humidity dew point Water must condense on something solid. There are no large solid surfaces in the air. However, the air is filled with tiny particles such as dust, smoke, and salt from the ocean. Water vapor condenses on these particles. CHAPTER RESOURCES SECTION OUTLINE

Most clouds form as air rises and cools. 16.3 Most clouds form as air rises and cools. Clouds are classified and named according to their altitudes, the ways they form, and their general characteristics. • Cirrus (SEER–uhs) means "curl of hair." Cirrus clouds appear feathery or wispy. Cirrus clouds form in very cold air at high altitudes and are made of ice crystals. • Cumulus (KYOOM–yuh–luhs) means "heap" or "pile." Cumulus-type clouds can grow to be very tall. The tallest clouds are cumulonimbus clouds, or thunderheads. These clouds produce thunderstorms that drop heavy rainfall. evaporation condensation precipitation humidity saturation relative humidity dew point CHAPTER RESOURCES SECTION OUTLINE

Most clouds form as air rises and cools. 16.3 Most clouds form as air rises and cools. • Stratus (STRAT–uhs) means "spread out." Stratus-type clouds form in flat layers. They form in layers when air cools over a large area without rising or when the air is gently lifted. Stratus clouds are smooth because they form without strong air movement. Some low stratus clouds are so dark that they completely block out the Sun. These clouds produce steady, light precipitation—unlike the brief showers that come from cumulus clouds. evaporation condensation precipitation humidity saturation relative humidity dew point CHAPTER RESOURCES SECTION OUTLINE

Most clouds form as air rises and cools. 16.3 Most clouds form as air rises and cools. Fog is a cloud that rests on the ground or a body of water. Like stratus clouds, fog has a smooth appearance. It usually forms when a surface is colder than the air above it. Water vapor in the air condenses as it cools, forming a thick mist. Fog on land tends to be heaviest at dawn, after the ground has cooled overnight. It clears as the ground is heated up by sunlight. evaporation condensation precipitation humidity saturation relative humidity dew point CHAPTER RESOURCES SECTION OUTLINE

Water falls to Earth’s surface as precipitation. 16.4 Water falls to Earth’s surface as precipitation. Water droplets in clouds merge to form raindrops. freezing rain sleet hail Ice crystals in clouds can form snow, rain, and other types of precipitation. acid rain Freezing rain is rain that freezes when it hits the ground or other surfaces. Sleet is rain that freezes into ice pellets while falling through cold air. Snow forms from ice crystals that merge in clouds. Hail forms when ice pellets move up and down in clouds, growing larger as they gain layers of ice. CHAPTER RESOURCES SECTION OUTLINE

Water falls to Earth’s surface as precipitation. 16.4 Water falls to Earth’s surface as precipitation. When the temperature inside a cloud is below freezing, water vapor changes into tiny ice crystals. The crystals grow by collecting more water vapor or by colliding and merging with one another. Snow isn't the only type of precipitation that forms this way. freezing rain sleet hail acid rain *Most rain in the United States actually starts out as falling ice crystals. Before the crystals reach the ground, they melt in a layer of warm air. CHAPTER RESOURCES SECTION OUTLINE

Water falls to Earth’s surface as precipitation. 16.4 Water falls to Earth’s surface as precipitation. Precipitation can carry pollution. Factories, power plants, automobiles, and some natural sources release sulfur dioxide and nitrogen oxides into the air. freezing rain sleet hail acid rain These gases can combine with water vapor to form sulfuric acid and nitric acid. The acids mix with cloud droplets or ice crystals that eventually fall to Earth's surface as precipitation. CHAPTER RESOURCES SECTION OUTLINE

16.1 The atmosphere's air pressure changes. I. The atmosphere's air pressure changes. air pressure A. Air exerts pressure. barometer B. Air pressure is related to altitude and density. 1. Pressure and Air Motion 2. Barometers and Air Pressure CHAPTER RESOURCES KEY CONCEPT SUMMARY

The atmosphere has wind patterns. 16.2 The atmosphere has wind patterns. II. The atmosphere has wind patterns. weather A. Uneven heating causes air to move. wind B. Earth’s rotation affects wind direction. global wind C. Bands of calm air separate global wind belts. Coriolis effect 1. Calm Regions jet stream 2. Wind Belts monsoon 3. Effects of Wind on Travel D. Jet streams flow near the top of the troposphere. E. Patterns of heating and cooling cause local winds and monsoons. CHAPTER RESOURCES 1. Local Winds 2. Monsoons KEY CONCEPT SUMMARY

Most clouds form as air rises and cools. 16.3 Most clouds form as air rises and cools. III. Most clouds form as air rises and cools. evaporation A. Temperature affects water in the air. condensation 1. Water in the Air precipitation 2. Humidity and Relative Humidity humidity B. Water vapor condenses and forms clouds. saturation 1. Characteristics of Clouds relative humidity 2. Cirrus Clouds dew point 3. Cumulus Clouds 4. Stratus Clouds CHAPTER RESOURCES 5. Fog KEY CONCEPT SUMMARY

Water falls to Earth’s surface as precipitation. 16.4 Water falls to Earth’s surface as precipitation. IV. Water falls to Earth’s surface as precipitation. freezing rain A. Precipitation forms from water droplets or ice crystals. sleet hail 1. Measuring Precipitation acid rain 2. Types of Precipitation B. Precipitation can carry pollution. CHAPTER RESOURCES KEY CONCEPT SUMMARY

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