chapter 13: the nature of storms earth science geology, the environment and the universe

Chapter 13: The Nature of StormsChapter 13: The Nature of Storms

EARTH SCIENCEGeology, the Environment and the Universe

Section 13.1 Thunderstorms

Section 13.2 Severe Weather

Section 13.3 Tropical Storms

Section 13.4 Recurrent Weather

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CHAPTER

13 Table Of Contents

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

ThunderstormsSECTION13.1

• The intensity and duration of thunderstorms depend on the local conditions that create them.

New Vocabularyair-mass thunderstorm

mountain thunderstorm

sea-breeze thunderstorm

frontal thunderstorm

stepped leader

return stroke


Up to 2000 thunderstorms are in progress around the world


• Both geography and air mass movements make thunderstorms most common in the southeastern United States.


• For a thunderstorm to form, three conditions must exist: a source of moisture, lifting of the air mass, and an unstable atmosphere.


How thunderstorms form

Limits to thunderstorm growth


TROPOPAUSE

• 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: air-mass and frontal.

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.



• Mountain thunderstorms occur when an air mass rises by orographic lifting, which involves air moving up the side of a mountain.




• Sea-breeze thunderstorms are local air-mass thunderstorms that occur because land and water store and release thermal energy differently.




• Frontal thunderstorms are produced by advancing cold fronts and, more rarely, warm fronts.

Frontal thunderstorms



• 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.

Thunderstorm Development


Please click the image above to view the video.


• Lightning is the transfer of electrical charge caused by the rapid rushes of air in a cumulonimbus cloud.


• 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.


Lightning Facts

Thunderstorms in the United States are most common in the Midwest.

a. true

b. false

Section CheckSECTION13.1

A mature thunderstorm has a region of updraft and a region of downdraft.

a. true

b. false


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.


Essential Questions

• Why are some thunderstorms more severe than others?

• What are the dangers of severe weather?

• How do tornadoes form?

Severe WeatherSECTION13.2

• air mass: large body of air that takes on the characteristics of the area over which it forms

• All thunderstorms produce wind, rain, and lightning, which can have dangerous and damaging effects under certain circumstances.

Review Vocabulary


New Vocabulary

supercell

downburst

tornado

Enhanced Fujita Tornado Damage scale


• Severe thunderstorms can develop into self-sustaining, extremely powerful storms called supercells.

• These furious storms can last for several hours and can have updrafts as strong as 240 km/h.

Supercells


Severe Thunderstorms

• An anvil-shaped cumulonimbus cloud is characteristic of many severe thunderstorms.


Supercells

Severe Thunderstorms

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.


Hail

• Hail is precipitation in the form of balls or lumps of ice. It forms because of two characteristics common to thunderstorms.


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.


Hail

• The second characteristic that allows hail to form is an abundance of strong updrafts and downdrafts moving side by side within a cloud.


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.


• 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.

Development of tornadoes


Tornadoes

Tornadoes

• The Enhanced Fujita Tornado Damage scale, which ranks tornadoes according to their destruction and estimated wind speed, is used to classify tornadoes.

Tornado classification


Please click the image above to view the interactive table.


Tornadoes

• 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.

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.

Tornado distribution


Tornadoes

Tornadoes

• 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.

Tornado safety


The strongest thunderstorms develop under highly stable atmospheric conditions.

a. true

b. false

SECTION13.2

Section Check

a. rain

b. snow

c. hail

d. sleet

Which type of precipitation requires strong updrafts and downdrafts to exist side by side in a cloud?

SECTION13.2

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.

SECTION13.2

Section Check

Essential Questions

• How do tropical cyclones form?

• What is the life cycle of a tropical cyclone?

• What are the dangers associated with hurricanes?

Tropical StormsSECTION13.3

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

• Normally peaceful, tropical oceans are capable of producing one of Earth’s most violent weather systems—the tropical cyclone.


New Vocabulary

tropical cyclone

eye

eyewall

Saffir-Simpson Hurricane Wind scale

storm surge


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.



• 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.

Cyclone location



• 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.

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.

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.



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.



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.



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.



Cyclone formation

Visualizing Cyclone Formation

• Like most storms, cyclones begin with warm moist air rising.



Tropical cyclone movement

• Like all large-scale storms, tropical cyclones move according to the wind currents that steer them.


Hurricane Hazards

• The Saffir-Simpson Hurricane Wind scale classifies hurricanes according to wind speed, which implies potential for flooding and potential for property damage.


Damage

• Hurricanes can cause extensive damage, particularly along coastal areas, which tend to be where human populations are the most dense.

Tropical Storms

Hurricane Hazards

SECTION13.3

Winds

• Much of the damage caused by hurricanes is associated with violent winds.


Hurricane Hazards

• A storm surge occurs when hurricane-force winds drive a mound of ocean water toward coastal areas where it washes over the land.

Storm surge


Hurricane Hazards

• 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.

Hurricane advisories and safety


Hurricane Hazards

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


What weather condition usually exists within the eye of a hurricane?

a. high wind

b. calm wind

c. tornadoes

d. lightning


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.


• What are the problems associated with recurring weather patterns?

• What atmospheric events cause recurring weather patterns?

• How do heat waves and cold waves differ?

Essential Questions

Recurrent WeatherSECTION13.4

Review Vocabulary

• Fahrenheit scale: a temperature scale in which water freezes at 32 and boils at 212

• Even a relatively mild weather system can become destructive and dangerous if it persists for long periods of time.


drought

heat wave

cold wave

windchill index

New Vocabulary


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.


• 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.

Floods


Droughts

• Droughts are extended periods of well-below-average 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.


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.


Droughts

• 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 high-pressure systems that cause 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.

Droughts

Heat waves


Please click the image above to view the interactive table.


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, high-pressure systems. However, cold waves are caused by systems of continental polar or arctic origin.


• 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.

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.

Cold Waves


• 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.

Cold Waves

Windchill index


• The windchill chart was designed to show the dangers of cold and wind.


Cold Waves

Windchill index

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


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.


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 Assessment Questions

Standardized Test Practice

Study Guide

Earth Science Online

Resources

CHAPTER

13 The Nature of Storms

• 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.

Study Guide

SECTION13.1

Thunderstorms

• 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.

Study Guide

SECTION13.1

Thunderstorms

• 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.

SECTION13.2

Severe Weather

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.

SECTION13.2

Severe Weather

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.

SECTION13.3

Tropical Storms

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.

SECTION13.3

Tropical Storms

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.

SECTION13.4

Recurrent Weather

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.

SECTION13.4

Recurrent Weather

Study Guide

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


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


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


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


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


Chapter Assessment

What forms as superheated air expands and produces a shock wave?

a. lightning

b. thunder

c. tornado

d. microburst

CHAPTER



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



a. north side

b. west side

c. south side

d. east side

On which side of a northern hemisphere tropical cyclone does the wind blow from the south?

CHAPTER



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



Why do hailstones consist of concentric layers?

CHAPTER



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.

CHAPTER



chapter 13: the nature of storms earth science geology, the environment and the universe

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mountain thunderstorms

overview of thunderstorms

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