4 7 severe storms (earth science)

Vocabulary hurricane storm surge tornado tropical depression tropical storm vortex Picture Credits Every effort has been made to secure permission and provide appropriate credit for phot

Trang 1

Scott Foresman Science 4.7

Nonfi ction Main Idea and Details • Maps

• Diagrams

• Text Boxes

• Glossary

Severe Storms

ISBN 0-328-13878-9 ì<(sk$m)=bdihie< +^-Ä-U-Ä-U

Scott Foresman Science 4.7

Nonfi ction Main Idea and Details • Maps

• Diagrams

• Text Boxes

• Glossary

Severe Storms

ISBN 0-328-13878-9 ì<(sk$m)=bdihie< +^-Ä-U-Ä-U

Trang 2

1 Where does a hurricane’s energy

come from?

2 What makes a hurricane an example

of a system?

3 What is the difference between a tornado

watch and a tornado warning?

4 Hurricanes are very

destructive, but they can also be helpful in some ways Explain some ways in which hurricanes are harmful and some ways in which hurricanes are helpful Use examples from the book to support your answer

5 Main Idea and Details Give the main

idea of how hurricanes are different from tornadoes Include supporting details

What did you learn?

Vocabulary

hurricane

storm surge

tornado

tropical depression

tropical storm

vortex

Picture Credits

Every effort has been made to secure permission and provide appropriate credit for photographic material

The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).

Opener: Getty Images; 2 Steve Starr/Corbis; 3 NOAA/OSEI; 6 Getty Images; 7 Warren Faidley/Photolibrary/OSF Limited;

9 Jim Reed/Corbis; 10 Getty Images; 12 (BL) Ray Soto/Corbis, (TL) Robert Preston/Alamy Images; 13 ©David R Frazier/

Photo Researchers, Inc.

ISBN: 0-328-13878-9

This publication is protected by Copyright, and permission should be obtained from the publisher prior to any

prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,

mechanical, photocopying, recording, or likewise For information regarding permission(s), write to

Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

by Colin Kong

Trang 3

Hurricanes

A hurricane is a storm with

a lot of energy This energy comes from warm ocean water

Hurricanes can be part of

a tropical storm system

Tropical Storms Become Hurricanes

Some storms form in areas near the equator The areas around the equator are called the tropics The storms that form in these areas are called tropical storms When tropical storms grow larger and stronger, they can become

hurricanes A hurricane is a

dangerous kind of storm that has wind speeds of at least

119 kilometers per hour

A hurricane is made up of many groups of thunderstorms

These thunderstorms wrap around the center of

a hurricane

3

In September 1999, there was a very strong hurricane

This hurricane was originally a tropical storm in the Atlantic Ocean People named it Floyd When the storm grew more powerful, it became Hurricane Floyd

Floyd moved across the ocean and crashed into the Bahamas Some reports from the Bahamas told of waves that reached a height of fi fty feet Then the storm hit North Carolina It was here that it did the most damage

Although Floyd became weaker as it moved across land, its huge size was still a problem The heavy rainfall from the hurricane covered a greater area than usual for a hurricane It also lasted longer than expected

Hurricane Floyd caused fi fty-one deaths in North Carolina It destroyed seven thousand homes and damaged thousands more Rebuilding after Floyd was costly

This satellite map shows the path of Hurricane Floyd along the East Coast of the United States.

ATLANTIC OCEAN

NORTH CAROLINA SOUTH

CAROLINA GEORGIA

FLORIDA

Trang 4

A tropical storm needs certain conditions in order

to form It needs a lot of warm ocean water An area of

low pressure at the ocean’s surface is also important

Winds blow toward this area of low pressure Then,

the ocean provides heat and water vapor As warm and

moist air rises, water vapor condenses Clouds form

These clouds sometimes become thunderstorms

Water vapor releases heat energy when it condenses

This makes the air warmer, and the storms grow

Warm air high above the ocean moves away from the

thunderstorms A tropical depression occurs when

winds grow stronger and begin to swirl If the winds

blow even faster, a tropical storm forms Winds in a

tropical storm move faster than sixty-two kilometers

per hour

How Tropical Storms Form

Winds blow faster and begin to swirl, forming

a tropical depression.

Thunderstorms develop over

warm areas of low pressure

near the ocean’s surface.

4

A Hurricane System

Thunderstorms move toward the area of lowest air pressure More air moves out from the top of the storm than moves in at the ocean’s surface Air pressure becomes lower The winds at the ocean’s surface blow faster toward the center of the storm The tropical storm turns into a hurricane when the winds reach

119 kilometers per hour

Parts that work together form a system The atmosphere and the ocean, two systems of Earth, work together to form a hurricane Hurricanes form in the atmosphere, but they get their energy from the ocean

Hurricanes can affect many of Earth’s systems

Their winds make large waves in the ocean When they are over land, hurricanes can uproot trees, destroy houses, and change the shape of the coast

Wind speed continues to increase

Pressure at the ocean’s surface drops, causing a tropical storm.

The winds reach 119 kilometers per hour The storm becomes

a fully developed hurricane.

5

Trang 5

Hurricane Classifi cation

Hurricanes are very powerful Their strong winds can blow

down large trees, tear down houses, and pick up cars

Hurricanes are categorized by their wind speed.

(kilometers per hour)

The center of a hurricane is called the eye The eye

is about twenty to fi fty kilometers wide The winds in

the eye are not strong The groups of thunderstorms

right around the eye have the strongest winds They also

have very heavy rains Winds on one side of the eye

blow in one direction Winds on the other side of the

eye blow in the opposite direction

People in the area under the hurricane’s eye may

think that the storm has passed They will soon fi nd

out that the second half of the hurricane is coming

The Eye of the Hurricane

The center spot of a hurricane is the eye

The entire hurricane spins around it.

6

A hurricane’s strong rains can cause problems

If a hurricane moves slowly over land, that area will get

a lot of rainfall The rain can fl ood roads and buildings

It can make lakes and rivers overfl ow Rain can also cause mudslides These fl oods and mudslides can cause deaths

Winds of a hurricane can create large waves on the

ocean A storm surge is an unusual rise in sea level

caused by the storm’s winds A storm surge is dangerous because the large amount of water can act as a bulldozer

It can sweep everything away that is in its path A surge can even kill people

Hurricanes are usually known as destroyers, but they can be helpful in some ways as well The rains fi ll up lakes, rivers, and streams They water plants and also prevent wildfi res because forests are no longer so dry

Wind and Water in a Hurricane

A storm surge crashes against a bridge.

7

Trang 6

Today scientists called meteorologists have tools

that can track hurricanes Instruments all over the world

collect data about hurricanes

Far above Earth’s surface, satellites track a storm’s

size, location, and wind speed Special planes fl y into

hurricanes to gather data Scientists then put the data

into a computer The computer develops a model to

forecast the weather that the hurricane will cause

A model represents a system or set of events Models

help people study objects that are too big, too diffi cult

to predict, or too dangerous to study directly

With a computer model, people can predict a

hurricane’s strength, direction, and speed But even

with the help of the computer, scientists

still need to use their knowledge and

experience to make a forecast

Predicting Hurricanes

Hurricane models are very useful They predict the storm’s path and show the location of the hurricane

The models also show where the storm is heading

Teamwork of Scientists

It takes more than one scientist to predict and track hurricanes One group of scientists may focus only

on pressures in the atmosphere A second group may improve the computer models Others may study water temperatures and how they affect a hurricane’s movement Scientists from different parts of the world may work together to improve forecasts

Meteorologists use computers

to make forecasts about hurricanes.

Trang 7

Tornadoes

A tornado is part of a strong

thunderstorm Many tornadoes form

in the midwestern United States

How Tornadoes Form

A funnel cloud is a rapidly spinning

column of air that comes out of a strong

thunderstorm It turns into a tornado when

it touches the ground Tornadoes usually

have winds that are less than two hundred

kilometers per hour Strong tornadoes can,

however, have winds that reach speeds of

fi ve hundred kilometers per hour These are

some of the fastest winds on Earth Most

tornadoes develop in the spring and summer

Tornadoes form when the inside of

a thunderstorm spins Next, a narrower

column of air starts to spin even faster

This column becomes a tornado when

it touches the ground Sometimes

tornadoes can come from the groups

of thunderstorms in a hurricane

11

The Vortex

A vortex is an area where air or liquid spins in a spiral or circular motion When you drain a full bathtub, you can see a small vortex

of water A tornado is a vortex formed

in a thunderstorm The outside of the tornado has air swirling upward

There is very low air pressure at the center of a tornado Air rushes into this low pressure area Water vapor condenses

along the outside of the tornado Then, a funnel

cloud may form below the base of the storm

The funnel cloud gathers dust and almost any object in its way All this material may make it easier to see the vortex But if there are heavy rains, large dust clouds, or darkness, people may still be unable to see the tornado

The vortex forms a funnel that narrows as it nears the ground.

Trang 8

A dust devil is not a tornado It is not even part of a thunderstorm

It is a column of swirling air

It can form on a clear day

A dust devil has much slower winds than a tornado has Its winds are approximately ninety-fi ve kilometers per hour Dust devils are most often found in deserts

Dust Devil

Waterspout

A waterspout is a rapidly spinning column of air

It forms over a lake or ocean

Its vortex lifts water droplets from the body of water

it is over Waterspouts are connected to clouds

A waterspout can be a tornado that has just moved from the land to the water

Waterspouts are often not

as strong as tornadoes

12

Tornado Forecasts

Warm, moist air masses collide with cold air masses

to form strong thunderstorms Only some strong thunderstorms become tornadoes It is diffi cult

to predict a tornado Tornadoes form and move very quickly There is not always much time to warn people about them

Tornadoes usually destroy everything in their path Scientists who study tornadoes take great risks to get close to tornadoes and learn more about them

Doppler radar is an instrument that identifi es the direction and speed of wind It also tells scientists about the vortex of a tornado

Doppler radar tower

Tornado Classifi cation

Scientist T Theodore Fujita developed a scale to classify tornadoes The scale measures the wind speed of a tornado and the amount of damage caused by strong winds.

(kilometers per hour)

13

Trang 9

The National Weather Service notifi es people about

tornadoes It sends out information on the radio and

television A tornado watch means that a tornado is

likely to form within a few hours A tornado warning

means that a person or a weather instrument has seen

a tornado

It is very important to take cover when there

is a tornado warning in your area Try to go

inside a building or take cover

in a basement If there is no

basement in the building, go

into a small room such as a

bathroom, closet, or hallway

If you are stuck outside, lie

fl at in a low area with your

head covered Do not stay

inside a car A tornado

can move faster than

a car It can even pick

up a car and throw it

Safety

Tornadoes can cause devastation Listen to advice on the radio and television about how to stay safe if a tornado strikes.

14

Hurricanes and Tornadoes

Hurricanes and tornadoes are very strong, dangerous storms Both storms spin around a center of low

air pressure Their strong winds cause a lot of damage

Hurricanes and tornadoes are also very different

in many ways A hurricane is wider than a tornado

It can be hundreds of kilometers wide, while a tornado

is usually not more than one hundred meters wide

A hurricane contains many thunderstorms, while a tornado comes from one thunderstorm Hurricanes form over water, while almost all tornadoes form over land A big difference between a hurricane and a tornado

is how long each storm lasts A hurricane can last for many days or even weeks A tornado lasts for only

a few minutes, but a tornado’s winds can be much stronger than a hurricane’s winds

Hurricanes form over the sea

When they move over land, tornadoes can develop.

15

Trang 10

Glossary

at least 119 kilometers per hour that is composed of many groups

of thunderstorms

caused by a storm’s winds

air that comes down from a thunderstorm and touches the ground

tropical depression a storm with swirling winds

and rains that is stronger than

a disturbance but weaker than

a storm

with wind speeds faster than sixty-two kilometers per hour

or swirls