5 6 weather (earth sciences)

California Leveled Science Readers (Grade 5) Content leveled readers teach science concepts, vocabulary, and reading skills – at each student’s reading level – and allow students to read and explore the wonders of nonfiction. Leveled science readers deliver science content to help address the individual needs of all students. They reinforce reading skills and strategies while promoting science understanding. Each grade 5 science reader is a richly illustrated, selfcontained little book with 10 to 14 double pages. BELOW 5.1 Building Blocks of Matter (Physical Sciences) 5.2 Changes in Matter (Physical Sciences) 5.3 Basic Structures of Organisms (Life Sciences) 5.4 MISSING 5.5 Water on Earth (Earth Sciences) 5.6 Weather (Earth Sciences) 5.7 The Solar System (Earth Sciences) ON 5.1 Understanding Matter (Physical Sciences) 5.2 How Matter Changes (Physical Sciences) 5.3 The Building Blocks of Organisms (Life Sciences) 5.4 Systems of the Human Body (Life Sciences) 5.5 Earths Hydrosphere (Earth Sciences) 5.6 How Weather Works (Earth Sciences) 5.7 Earths Solar System (Earth Sciences) ADVANCED 5.1 Atoms (Physical Sciences) 5.2 Acids and Bases at Work (Physical Sciences) 5.3 MISSING 5.4 MISSING 5.5 MISSING 5.6 Hurricanes (Earth Sciences) 5.7 The Red Planet (Earth Sciences)

Genre Comprehension Skill Text Features Science Content

• Labels

• Charts

• Glossary

Weather

Scott Foresman Science 5.6

Standards Preview Standard Set 4 Earth Sciences

4 Energy from the Sun heats Earth

unevenly, causing air movements that

result in changing weather patterns

As a basis for understanding this

concept:

4.a Students know uneven heating

of Earth causes air movements

(convection currents).

4.b Students know the influence that

the ocean has on the weather and

the role that the water cycle plays in

weather patterns.

4.c Students know the causes and

effects of different types of severe weather.

4.d Students know how to use

weather maps and data to predict local weather and know that weather forecasts depend on many variables.

4.e Students know that the Earth’s

atmosphere exerts a pressure that decreases with distance above Earth’s surface and that at any point it exerts this pressure equally in all directions.

ISBN 0-328-23467-2 ì<(sk$m)=cdeghh< +^-Ä-U-Ä-U

by Mary Imani

Earth Sciences

air mass

anemometer

atmospheric pressure

barometer

convection current

cyclone

front

rain gauge

tempered

wind

Picture Credits

Illustration

6, 8, 23 Studio Liddell; 14 Tony Randazzo

Photographs

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.

Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson.

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

2 (R) ©Dorling Kindersley; 15 ©Japan Meteorological Agency

ISBN: 0-328-23467-2

Copyright © Pearson Education, Inc All Rights Reserved Printed in the United States of America

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,

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

1 2 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06

by Mary Imani

How does

air move?

Under Pressure

The air surrounding Earth

makes up the atmosphere Look at

the diagram Earth’s atmosphere

has several levels Most weather

takes place in the lowest level This

level is nearest Earth’s surface

Atmospheric pressure,

or air pressure, is the weight of

air pushing down on an area

Atmospheric pressure changes

as you go higher or lower in the

atmosphere This is because there

are different amounts of air at each

level in the atmosphere As you

go up, the pressure decreases It

increases as you go down

Air pressure is lower

at this level The air particles can spread farther apart There is less air above to push them together.

Air pressure is lowest

at this level The air particles are farthest apart.

Air pressure is highest near the ground The weight of the air above presses the air near Earth’s surface close together.

3

More About Atmospheric Pressure

Air is matter Although it is invisible, it has mass and takes up space Gravity pulls air toward Earth’s surface Air has weight because of the pull of gravity The weight of the air causes air pressure

Air particles are always moving in every direction

As you move away from Earth’s surface, the air particles become more spread out This means that high up in Earth’s atmosphere, air pressure is lower than it is at Earth’s surface

An altimeter measures air pressure to give an object’s altitude

Convection Currents

Gas particles are closer together in cool air than in

warm air This makes a difference in the weight of air Cool

air is heavier than warm air

The Sun heats Earth’s surface unevenly This leads to

different air temperatures Land heats up and cools off

faster than water This causes the air over the land to have

a different temperature than air over the water

Differences in air temperature cause

convection currents to form Suppose

cool air and warm air are next to each

other The heavier cool air will sink

The lighter warm air will rise A

convection current will be formed

A convection current is the

rising and sinking of matter in

a circular pattern

Rising air will cool This cooled air is pushed over the water by the rising air below it.

As the cool air sinks below the warm air, wind is created.

The cool water

won’t warm the

air above it as

much as the land

warms the air

above it.

As the diagram shows, wind is produced by convection

currents in the air Wind is movement of air that happens

because of differences in air pressure caused by temperature differences

The kind of convection current shown in the diagram occurs during the day It forms near oceans and large lakes

A different kind of convection current takes place at night

It fl ows in the opposite direction

The circular pattern of sinking cool air and rising warm air repeats over and over This pattern causes rain and changes in air pressure These circular air currents can even cause the patterns you see in clouds

Convection currents are not limited to the air They are also found in ocean water and the rocks deep beneath Earth’s surface The convection currents inside Earth move heat toward the surface In the oceans, convection currents create ocean currents The ocean currents, in turn, infl uence different climates

The warm land makes air above

it warm This warm air is forced

up by the cool air.

5

Uneven Heating Due to Earth’s Tilt

Earth’s surface and atmosphere are heated by energy

from the Sun But this heating is uneven The uneven

heating leads to differences in air temperature These

differences create Earth’s convection currents, which affect

weather and climate

Huge convection currents form

above Earth They are created

when air masses with different

temperatures meet These currents

shape wind patterns.

7

Earth orbits the Sun As it orbits, it also spins around its axis Earth’s axis is tilted at an angle of about 23.5° This tilt has a huge effect

Because of the tilt, the Sun’s rays hit some regions on Earth more directly than others Near the equator, the Sun

is always high in the sky The Sun’s rays hit these regions at

a direct angle Near the poles, the Sun is always low in the sky The Sun’s rays hit these regions at a less direct angle

How do you think the angle at which the Sun’s rays strike the equator and poles affects these regions’ weather?

Check your answer by reading the captions in the diagram

Earth’s axis

The equator

The North Pole

The South Pole

Near the poles, the Sun’s rays are more spread out.

Near the equator, the Sun’s rays hit more directly.

What are air masses?

Kinds of Air Masses

Sometimes air will stay over an area for a period of

time As it does, it takes on the properties of that area

If the air stays long enough, it becomes an air mass An

air mass is a large body of air with similar properties

all through it The two most important properties are

temperature and the amount of water vapor The weather

your area experiences usually depends on the air masses

that are above it There is some weather that happens only

along the edges of air masses

Air masses move because of winds near or far above the

ground The jet stream is a strong wind, high above Earth

It can move cold, dry air from Canada to the United States

Cooler air forces warmer air

to move up quickly.

Cold Front

Warm air Cold air

There are four basic kinds of air masses They are named for the areas where they form Maritime polar air masses form over the oceans near the poles These air masses are cold and fairly moist Continental tropical air masses form over large hot deserts The air in them is warm and dry Maritime tropical air masses form over tropical oceans or rain forests They are warm and very humid, containing a lot of evaporated water Finally, continental polar air masses are made over the land and ice at the poles This air is cold and dry

When Air Masses Meet

A front is a boundary between two air masses There

are cold fronts, warm fronts, and stationary fronts Colder

air is brought into an area by cold fronts Warmer air is brought into an area by warm fronts A stationary front

moves very slowly or not at all

Warmer air gradually rises above the cooler air.

Cold air Warm air

Warm Front

9

Highs and Lows

Have you ever noticed the letters H and L on a weather

map? The H shows where there is high pressure The L

shows where there is low pressure Wind fl ows from areas of

higher pressure to areas of lower pressure

Atmospheric pressure is affected by air temperature Air

that is cool is heavier It is under higher pressure than the

same volume of warmer air Air that is warm is lighter It is

under lower pressure than cooler air

Fair weather is usually brought in by areas of high

pressure Cloudy and stormy weather often comes with

areas of low pressure Low-pressure systems may also bring

rain or snow

Anticyclone

11

Cyclones

High-pressure air wraps around warm, low-pressure air

The high pressure makes the warm air in the center rise As the air rises, the surrounding high–pressure air fl ows in to

take its place This fl ow of air forms a wind called a cyclone

The cyclone spirals inward and forms a weather system In other words, it moves in a spiral

Earth’s rotation causes cyclone winds to spin counterclockwise in the United States South of the equator, cyclone winds fl ow in a clockwise direction

Stormy weather is usually found near cyclones A hurricane is a severe form of a cyclone

Anticyclones spin clockwise north of the equator, in the opposite direction of cyclones They usually cause clear weather

In the United States, cyclone winds spin counterclockwise.

Cyclone

What causes severe

weather?

Thunderstorms

The pictures on this page show how a thunderstorm

can form In the fi rst stage, strong currents of moist air

rise Water condenses, building clouds in the rising air The

clouds are made up of ice crystals and water droplets In

the second stage, precipitation starts to fall This pulls some

air downward as other air currents rise In the storm’s last

stage, all the air moves downward Precipitation leaves the

clouds Note that two parts of the water cycle, condensation

and precipitation, are involved in thunderstorms

First stage:

All air currents move upward.

13

Different areas of a thunderstorm cloud have positive or negative charges

The cloud’s negative charges cause positive charges to gather on the ground.

Second stage:

Air currents are mixed.

Final stage:

All air currents move downward.

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Tornadoes

Some thunderstorms can produce tornadoes A tornado

is a violently rotating column of air It reaches from a

thunderstorm to the ground

Tornadoes move fast The winds inside of them travel at

hundreds of kilometers per hour Tornado winds can throw

cars around They can severely damage buildings

Take cover right away if you hear a tornado warning

on the radio or television If you can, go to a basement

Otherwise, go to a closet You can also take shelter in a

windowless room in the center of a building

Before tornadoes form, winds change

direction and increase in speed

Winds begin to spin.

As the tornado forms, air within it

rises The spinning air begins to tilt

upward

The spinning area grows wider.

15

Hurricanes

Hurricanes are ocean storms They get their energy from warm ocean water How?

Remember, water vapor from the ocean condenses during the water cycle When water vapor condenses,

it gives off heat If conditions are right, the heat energy builds It gets strong enough to drive hurricane winds

Hurricanes are very severe storms They can be hundreds of kilometers wide and hit several countries

Hurricanes last for days They produce huge waves, which pound the shores and can cause fl oods Heavy rains from a hurricane can also produce fl oods far inland

Thunderstorms grow out of a tropical depression.

Thunderstorms begin to move in spiral bands Air pressure drops lower, and surface winds blow faster The tropical storm is now a hurricane.

Air pressure at the ocean’s surface drops Surface winds blow faster and begin to swirl A tropical storm develops.

Ocean Temperature Affects Weather

Changes in the ocean’s temperature can cause large

changes in weather El Niño is a warming of the eastern

Pacifi c Ocean near the equator that takes place every 4

to 12 years This change can cause very wet and very dry

seasons in many parts of the world

As you know, land heats and cools more quickly than

water This means air above land heats and cools more

quickly than air above water Large bodies of water, such as

oceans, can affect air temperature The air above oceans is

tempered It is warmed in winter and cooled in summer.

Very heavy rains fall during the summer monsoon season.

16

Monsoons

Remember that in the United States, winds and weather usually fl ow from west to east But in some parts of the world, wind direction changes with the seasons A monsoon

is a wind that changes directions with the seasons

Monsoons are common in south and southeastern Asia

Asia’s winter monsoons form when land temperatures become colder than ocean temperatures The colder land temperatures cause areas of high pressure to form Wind

fl ows from these areas to the lower pressure areas over the ocean Because the land air is dry, the winter monsoon brings little rain

17

How are weather

forecasts made?

Collecting Data

To fully describe the weather, you must describe

all its parts The most important weather features are

temperature, moisture, clouds, precipitation, wind speed, air

pressure, and wind direction All these parts may interact

with one another They may also change completely in a

very short time

Rain Gauge

Barometer

19

Many weather instruments measure the changing parts

of the weather, called variables A barometer shows air

pressure Some barometers work by having air pressure raise and lower an amount of mercury inside of a tube A hygrometer measures the amount of evaporated water in the air The length of its horsehair tells how humid it is

An anemometer measures wind speed A rain gauge

measures how much rain has fallen

Doppler radar can measure the winds and precipitation inside a storm The radar sends out energy Some of the energy bounces off storm parts, such as raindrops, and returns to the radar The returning energy shows the raindrops’ direction and speed

Doppler radar is an important new weather technology It is used to fi nd “ordinary”

storms and track their motion It is also used to track tornadoes

Anemometer