Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
EARTH SCIENCE Geology, the Environment and the Universe Chapter 13: The Nature of Storms CHAPTER 13 Table Of Contents Section 13.1 Thunderstorms Section 13.2 Severe Weather Section 13.3 Tropical Storms Section 13.4 Recurrent Weather Click a hyperlink to view the corresponding slides. Exit SECTION 13.1 Thunderstorms Essential Questions • How do thunderstorms form? • What are the different types of thunderstorms? • What is the life cycle of a thunderstorm? Review Vocabulary • latent heat: stored energy in water vapor that is not released to warm the atmosphere until condensation occurs SECTION 13.1 Thunderstorms • The intensity and duration of thunderstorms depend on the local conditions that create them. New Vocabulary air-mass thunderstorm mountain thunderstorm sea-breeze thunderstorm frontal thunderstorm stepped leader return stroke SECTION 13.1 Thunderstorms Up to 2000 thunderstorms are in progress around the world SECTION 13.1 Thunderstorms • Both geography and air mass movements make thunderstorms most common in the southeastern United States. SECTION 13.1 Thunderstorms How thunderstorms form • For a thunderstorm to form, three conditions must exist: a source of moisture, lifting of the air mass, and an unstable atmosphere. SECTION 13.1 Thunderstorms Limits to thunderstorm growth TROPOPAUSE SECTION 13.1 Thunderstorms Types of Thunderstorms • Thunderstorms are often classified according to the mechanism that causes the air mass that formed them to rise. • There are two main types of thunderstorms: airmass and frontal. SECTION 13.1 Thunderstorms Types of Thunderstorms Air-mass thunderstorms • When air rises because of unequal heating of Earth’s surface beneath one air mass, the thunderstorm is called an air-mass thunderstorm. • There are two kinds of air-mass thunderstorms. SECTION 13.1 Thunderstorms Types of Thunderstorms Air-mass thunderstorms • Mountain thunderstorms occur when an air mass rises by orographic lifting, which involves air moving up the side of a mountain. SECTION 13.1 Thunderstorms Types of Thunderstorms Air-mass thunderstorms • Sea-breeze thunderstorms are local air-mass thunderstorms that occur because land and water store and release thermal energy differently. SECTION 13.1 Thunderstorms Types of Thunderstorms Frontal thunderstorms • Frontal thunderstorms are produced by advancing cold fronts and, more rarely, warm fronts. SECTION 13.1 Thunderstorms Thunderstorm Development • A thunderstorm usually has three stages: the cumulus stage, the mature stage, and the dissipation stage. The stages are classified according to the direction the air is moving. SECTION 13.1 Thunderstorms Please click the image above to view the video. SECTION 13.1 Thunderstorms • Lightning is the transfer of electrical charge caused by the rapid rushes of air in a cumulonimbus cloud. SECTION 13.1 Thunderstorms Lightning Facts • A lightning bolt heats the surrounding air to about 30,000C, about five times hotter than the surface of the Sun. • Lightning natural creates Ozone. • Lightning kills 60 people a year. • The thunder you hear is the sound produced as this superheated air rapidly expands and contracts. SECTION Section Check 13.1 Thunderstorms in the United States are most common in the Midwest. a. true b. false SECTION Section Check 13.1 A mature thunderstorm has a region of updraft and a region of downdraft. a. true b. false SECTION 13.1 Section Check What is the difference between air-mass thunderstorms and frontal thunderstorms? Answer: Air-mass thunderstorms form as a result of uplift of air within one air mass. Frontal thunderstorms form as a result of uplift of air along frontal boundaries. SECTION 13.2 Severe Weather Essential Questions • Why are some thunderstorms more severe than others? • What are the dangers of severe weather? • How do tornadoes form? SECTION 13.2 Severe Weather • All thunderstorms produce wind, rain, and lightning, which can have dangerous and damaging effects under certain circumstances. Review Vocabulary • air mass: large body of air that takes on the characteristics of the area over which it forms SECTION 13.2 Severe Weather New Vocabulary supercell downburst tornado Enhanced Fujita Tornado Damage scale SECTION 13.2 Severe Weather Severe Thunderstorms Supercells • Severe thunderstorms can develop into selfsustaining, extremely powerful storms called supercells. • These furious storms can last for several hours and can have updrafts as strong as 240 km/h. SECTION 13.2 Severe Weather Severe Thunderstorms Supercells • An anvil-shaped cumulonimbus cloud is characteristic of many severe thunderstorms. SECTION 13.2 Severe Weather Strong Winds • Violent downdrafts that are concentrated in a local area are called downbursts. • Based on the size of the area they affect, downbursts are classified as either macrobursts or microbursts. SECTION 13.2 Severe Weather Hail • Hail is precipitation in the form of balls or lumps of ice. It forms because of two characteristics common to thunderstorms. SECTION 13.2 Severe Weather Hail • For hail to form, water droplets rise to the heights of a cumulonimbus cloud where the temperature is below freezing, encounter ice pellets, and freeze on contact with the pellets, which causes the ice pellets to grow larger. SECTION 13.2 Severe Weather Hail • The second characteristic that allows hail to form is an abundance of strong updrafts and downdrafts moving side by side within a cloud. SECTION 13.2 Severe Weather Tornadoes • A tornado is a violent, whirling column of air in contact with the ground. • When a tornado does not reach the ground, it is called a funnel cloud. SECTION 13.2 Severe Weather Tornadoes Development of tornadoes • A tornado forms when wind speed and direction change suddenly with height, a phenomenon called wind shear. • Although tornadoes rarely exceed 200 m in diameter and usually last only a few minutes, they can be extremely destructive. SECTION 13.2 Severe Weather Please click the image above to view the video. SECTION 13.2 Severe Weather Tornadoes Tornado classification • The Enhanced Fujita Tornado Damage scale, which ranks tornadoes according to their destruction and estimated wind speed, is used to classify tornadoes. SECTION 13.2 Severe Weather Please click the image above to view the interactive table. SECTION 13.2 Severe Weather Tornadoes Tornado distribution • Most tornadoes—especially violent ones— form in the spring during the late afternoon and evening, when the temperature contrasts between polar air and tropical air are the greatest. This type of large temperature contrast occurs most frequently in the central United States. SECTION 13.2 Severe Weather Tornadoes Tornado distribution • Many of the more than 1000 tornadoes that touch down in the United States each year occur in a region called “Tornado Alley,” which extends from northern Texas through Oklahoma, Kansas, and Missouri. SECTION 13.2 Severe Weather Tornadoes Tornado safety • If you are caught in a tornado, take shelter in the southwest corner of a basement, a small downstairs room or closet, or a tornado shelter. SECTION Section Check 13.2 The strongest thunderstorms develop under highly stable atmospheric conditions. a. true b. false SECTION Section Check 13.2 Which type of precipitation requires strong updrafts and downdrafts to exist side by side in a cloud? a. rain b. snow c. hail d. sleet SECTION 13.2 Section Check How do tornadoes form? Answer: The rotation of a tornado begins as a result of wind shear, wind at different levels of the atmosphere blowing in different directions or at different speeds. The horizontal rotation is then tilted to a vertical position by thunderstorm updrafts. A tornado forms if the rotating column extends to the ground. SECTION 13.3 Tropical Storms Essential Questions • How do tropical cyclones form? • What is the life cycle of a tropical cyclone? • What are the dangers associated with hurricanes? SECTION 13.3 Tropical Storms • Normally peaceful, tropical oceans are capable of producing one of Earth’s most violent weather systems—the tropical cyclone. Review Vocabulary • Coriolis effect: caused by Earth’s rotation, moving particles, such as air, are deflected to the right north of the equator, and to the left south of the equator SECTION 13.3 Tropical Storms New Vocabulary tropical cyclone eye eyewall Saffir-Simpson Hurricane Wind scale storm surge SECTION 13.3 Tropical Storms Overview of Tropical Cyclones • During summer and fall, the tropics experience conditions ideal for the formation of large, rotating, low-pressure tropical storms called tropical cyclones. SECTION 13.3 Tropical Storms Overview of Tropical Cyclones Cyclone location • Favorable conditions for cyclone formation exist in all tropical oceans except the South Atlantic Ocean and the Pacific Ocean off the west coast of South America. SECTION 13.3 Tropical Storms Please click the image above to view the video. SECTION 13.3 Tropical Storms Overview of Tropical Cyclones Cyclone formation • Tropical cyclones require two basic conditions to form: an abundant supply of warm ocean water and some sort of mechanism to lift warm air and keep it rising. SECTION 13.3 Tropical Storms Overview of Tropical Cyclones Cyclone formation • The first indication of a building tropical cyclone is a moving tropical disturbance. When a disturbance over a tropical ocean acquires a cyclonic circulation around a center of low pressure, it has reached the developmental stage and is known as a tropical depression. SECTION 13.3 Tropical Storms Overview of Tropical Cyclones Cyclone formation • When wind speeds around the low-pressure center of a tropical depression exceed 62 km/h, the system is called a tropical storm. • If air pressure continues to fall and winds around the center reach at least 119 km/h, the storm is officially classified as a cyclone. SECTION 13.3 Tropical Storms Overview of Tropical Cyclones Cyclone formation • Once winds reach at least 119 km/h, another phenomenon occurs—the development of a calm center of the storm called the eye. • The eye of the cyclone is often 30 to 60 km of calm weather and blue sky. SECTION 13.3 Tropical Storms Overview of Tropical Cyclones Cyclone formation • The strongest winds in a hurricane are usually concentrated in the eyewall—a tall band of strong winds and dense clouds that surrounds the eye. SECTION 13.3 Tropical Storms Overview of Tropical Cyclones Cyclone formation • A hurricane will last until it can no longer produce enough energy to sustain itself. This usually happens when the storm has moved either over land or over colder water. SECTION 13.3 Tropical Storms Visualizing Cyclone Formation • Like most storms, cyclones begin with warm moist air rising. SECTION 13.3 Tropical Storms Please click the image above to view the video. SECTION 13.3 Tropical Storms Overview of Tropical Cyclones Tropical cyclone movement • Like all large-scale storms, tropical cyclones move according to the wind currents that steer them. SECTION 13.3 Tropical Storms Hurricane Hazards • The Saffir-Simpson Hurricane Wind scale classifies hurricanes according to wind speed, which implies potential for flooding and potential for property damage. SECTION 13.3 Tropical Storms Hurricane Hazards Damage • Hurricanes can cause extensive damage, particularly along coastal areas, which tend to be where human populations are the most dense. SECTION 13.3 Tropical Storms Hurricane Hazards Winds • Much of the damage caused by hurricanes is associated with violent winds. SECTION 13.3 Tropical Storms Hurricane Hazards Storm surge • A storm surge occurs when hurricane-force winds drive a mound of ocean water toward coastal areas where it washes over the land. SECTION 13.3 Tropical Storms Hurricane Hazards Hurricane advisories and safety • The National Hurricane Center issues a hurricane warning at least 36 hours before a hurricane is predicted to strike. • Awareness, combined with proper safety precautions, has greatly reduced death tolls associated with hurricanes in recent years. SECTION 13.3 Section Check At what latitudes do tropical cyclones usually form? a. between 0 and 5 b. between 5 and 30 c. between 30 and 50 d. between 50 and 70 SECTION Section Check 13.3 What weather condition usually exists within the eye of a hurricane? a. high wind b. calm wind c. tornadoes d. lightning SECTION 13.3 Section Check What is the source of a hurricane’s energy? Answer: A hurricane’s energy comes from the warm water over which it develops. As ocean water evaporates, some heat is taken from the ocean. The water vapor then rises high into the atmosphere. The heat that was taken from the ocean is released to the atmosphere as the water vapor condenses. SECTION 13.4 Recurrent Weather Essential Questions • What are the problems associated with recurring weather patterns? • What atmospheric events cause recurring weather patterns? • How do heat waves and cold waves differ? SECTION 13.4 Recurrent Weather • Even a relatively mild weather system can become destructive and dangerous if it persists for long periods of time. Review Vocabulary • Fahrenheit scale: a temperature scale in which water freezes at 32 and boils at 212 SECTION 13.4 Recurrent Weather New Vocabulary drought heat wave cold wave windchill index SECTION 13.4 Recurrent Weather Floods • An individual thunderstorm can unleash enough rain to produce floods, and hurricanes also cause torrential downpours, which result in extensive flooding. • Floods can also occur when weather patterns cause even mild storms to persist over the same area. SECTION 13.4 Recurrent Weather Floods • Low-lying areas are most susceptible to flooding, making coastlines particularly vulnerable to storm surges during hurricanes. • Rivers in narrow-walled valleys can rise rapidly, creating high-powered and destructive walls of water. SECTION 13.4 Recurrent Weather Droughts • Droughts are extended periods of well-belowaverage rainfall. • Droughts are usually the result of shifts in global wind patterns that allow large, high-pressure systems to persist for weeks or months over continental areas. SECTION 13.4 Recurrent Weather Droughts • Because the sinking air prevents humid air from rising, condensation cannot occur, and drought sets in until global patterns shift enough to move the high-pressure system. SECTION 13.4 Recurrent Weather Droughts Heat waves • An unpleasant side effect of droughts often comes in the form of heat waves, which are extended periods of above-average temperatures. • Heat waves can be formed by the same highpressure systems that cause droughts. SECTION 13.4 Recurrent Weather Droughts Heat waves • Because of the dangers posed by a combination of heat and humidity, the National Weather Service (NWS) routinely reports the heat index. • The heat index assesses the effect of the body’s difficulty in regulating its internal temperature as relative humidity rises. SECTION 13.4 Recurrent Weather Please click the image above to view the interactive table. SECTION 13.4 Recurrent Weather Cold Waves • The opposite of a heat wave is a cold wave, which is an extended period of below-average temperatures. • Cold waves are also brought on by large, highpressure systems. However, cold waves are caused by systems of continental polar or arctic origin. SECTION 13.4 Recurrent Weather Cold Waves • Because of the location and the time of year in which they occur, winter high-pressure systems are much more influenced by the jet stream than are summer high-pressure systems. SECTION 13.4 Recurrent Weather Cold Waves • The winter location of the jet stream can remain essentially unchanged for days or even weeks. This means that several polar high-pressure systems can follow the same path and subject the same areas to continuous numbing cold. SECTION 13.4 Recurrent Weather Cold Waves Windchill index • The effects of cold air on the human body are magnified by wind. Known as the windchill factor, this phenomenon is measured by the windchill index. SECTION 13.4 Recurrent Weather Cold Waves Windchill index • The windchill chart was designed to show the dangers of cold and wind. SECTION Section Check 13.4 The temperature is 0F and the wind speed is 30 miles per hour. What is the windchill? a. –5F b. –10F c. –26F d. –58F SECTION 13.4 Section Check What happens to air at the center of a high-pressure system? a. It sinks and water vapor condenses. b. It sinks and water vapor resists condensation. c. It rises and water vapor condenses. d. It rises and water vapor resists condensation. SECTION 13.4 Section Check What conditions result in extensive flooding? Possible answer: The most extensive flooding occurs as a result of heavy and persistent rain, saturated soil, and low-lying ground. CHAPTER The Nature of Storms 13 Resources Earth Science Online Study Guide Chapter Assessment Questions Standardized Test Practice SECTION Thunderstorms 13.1 Study Guide • The intensity and duration of thunderstorms depend on the local conditions that create them. • The cumulus stage, the mature stage, and the dissipation stage comprise the life cycle of a thunderstorm. • Clouds form as water is condensed and latent heat is released. SECTION Thunderstorms 13.1 Study Guide • Thunderstorms can be produced either within air masses or along fronts. • From formation to dissipation, all thunderstorms go through the same stages. • Lightning is a natural result of thunderstorm formation. SECTION Severe Weather 13.2 Study Guide • All thunderstorms produce wind, rain, and lightning, which can have dangerous and damaging effects under certain circumstances. • Intense rotating updrafts are associated with supercells. • Downbursts are strong winds that result in damage associated with thunderstorms. SECTION Severe Weather 13.2 Study Guide • Hail is precipitation in the form of balls or lumps of ice that accompany severe storms. • The worst storm damage comes from a vortex of high winds that moves along the ground as a tornado. SECTION Tropical Storms 13.3 Study Guide • Normally peaceful, tropical oceans are capable of producing one of Earth’s most violent weather systems—the tropical cyclone. • Tropical cyclones rotate counterclockwise in the northern hemisphere. • Tropical cyclones are also known as hurricanes and typhoons. SECTION Tropical Storms 13.3 Study Guide • Tropical cyclones go through the same stages of formation and dissipation as other storms. • Tropical cyclones are moved by various wind systems after they form. • The most dangerous part of a tropical cyclone is the storm surge. • Hurricane alerts are given at least 36 hours before the hurricane arrives. SECTION Recurrent Weather 13.4 Study Guide • Even a relatively mild weather system can become destructive and dangerous if it persists for long periods of time. • Too much heat and too little precipitation causes droughts. • Too little heat and a stalled jet stream can cause weeks of cold weather in an area. SECTION Recurrent Weather 13.4 Study Guide • Heat index estimates the effect on the human body when the air is hot and the humidity is high. • Cold index tells how wind, humidity, and temperature affect your body in winter. • Windchill is a factor used to warn about the effect of cold air and wind on the human body. CHAPTER The Nature of Storms 13 Chapter Assessment Which weather event is often related to the presence of persistent high pressure over a region? a. a flood b. a drought c. a tornado d. a blizzard CHAPTER 13 The Nature of Storms Chapter Assessment Which type of movement describes the air flow in the eyewall of a hurricane? a. counterclockwise upward spiral b. clockwise upward spiral c. counterclockwise downward spiral d. clockwise downward spiral CHAPTER 13 The Nature of Storms Chapter Assessment Why do people feel less comfortable on a hot day when the humidity is high? a. The air is less dense. b. The air moves less. c. Less evaporation occurs. d. Less precipitation occurs. CHAPTER 13 The Nature of Storms Chapter Assessment Which type of thunderstorm could form as a result of the air circulation shown? a. mountain thunderstorm b. sea-breeze thunderstorm c. cold-front thunderstorm d. warm-front thunderstorm CHAPTER 13 The Nature of Storms Chapter Assessment What hazards do hurricanes cause when they make landfall? Possible answer: Hurricanes making landfall bring high wind, tornadoes, and sometimes severe lightning. Storm surge causes flooding along the coast, and heavy rain causes flooding inland. CHAPTER The Nature of Storms 13 Standardized Test Practice What forms as superheated air expands and produces a shock wave? a. lightning b. thunder c. tornado d. microburst CHAPTER 13 The Nature of Storms Standardized Test Practice What is the Saffir-Simpson scale? a. a scale for classifying tornadoes b. a scale for classifying hurricanes c. a scale for classifying thunderstorms d. a scale for classifying lightning CHAPTER 13 The Nature of Storms Standardized Test Practice On which side of a northern hemisphere tropical cyclone does the wind blow from the south? a. north side b. west side c. south side d. east side CHAPTER 13 The Nature of Storms Standardized Test Practice How is the life cycle of a supercell thunderstorm similar to the life cycle of a hurricane? Possible answer: Both storms form from energy supplied by rising moist air, and both storms dissipate when the supply of rising moist air is cut off. CHAPTER 13 The Nature of Storms Standardized Test Practice Why do hailstones consist of concentric layers? CHAPTER 13 The Nature of Storms Standardized Test Practice Possible answer: The layers form as hailstones are tossed in a thunderstorm by strong updrafts. A new layer of ice is added each time the hailstone moves into a level of supercooled water droplets. These water droplets exist at temperatures that are well below the normal freezing point of water and so change to ice as soon as they come into contact with the hailstone.