FOCUS ON EARTH SCIENCE (14)

Use colored pencils to draw the following scene on a sheet of paper: The Sun shining on Earth’s surface, which includes ocean water, land, lakes, rivers, and snow-capped mountains with

Weather and Climate

During winter—California’s rainy season—the hills turn green and valleys fill with thick, misty fog Fields of golden poppies—California’s state flower—can be seen each spring throughout the state During summer—California’s dry season—the hills turn golden brown How does California’s weather and climate contribute to its nickname—“the golden state?”

Many factors affect

weather and climate

often defined by annual

temperatures and

Start-Up Activities

465

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How does water move

in the atmosphere?

Water moves from oceans

to clouds to lakes and rivers

How does this happen?

Procedure

1 Use colored pencils to

draw the following scene

on a sheet of paper: The

Sun shining on Earth’s surface, which

includes ocean water, land, lakes, rivers,

and snow-capped mountains with some

clouds in the sky

2 Draw arrows on your diagram that show

how water moves from Earth’s surface

into the atmosphere and back

Think About This

• Infer Streams flow from melting snow,

run down the mountains, join other

streams, and become rivers Where do the

rivers end up?

• Explain The ocean does not continue to

fill until it spills over the land Where does

the ocean water go? Explain

STEP 1 Collect three sheets of paper and

layer them about 2 cm apart vertically Keep the left edges even

STEP 2 Fold up the bottom edges of the

paper to form 5 equal tabs Crease the fold

to hold the tabs in place

STEP 3 Staple along the fold Label as

Recognizing Cause and Effect

As you read Lesson 3, use your Foldable to record information about climates and the factors that influence climates

ca6.msscience.com

4.a

ELA6: R 2.2

Learn It! Good readers compare and contrast information as they read This means they look

for similarities and differences to help them to remember

important ideas Look for signal words in the text to let

you know when the author is comparing or contrasting.

Compare and Contrast Signal Words

at the same time although

in a similar way on the other hand

Practice It! Read the excerpt below and notice how the author uses contrast signal words to

describe the temperature differences between Newport

Beach and Big Bear.

On a sunny winter day, a person can be in Newport Beach, California, and observe the peaks of nearby mountains covered in snow, such as Big Bear

Beach and Big Bear, are nearly the same,

temperature.

Apply It! Compare and trast mediterranean and highland climates on page 484.

con-466

Target Your Reading

Use this to focus on the main ideas as you read the chapter.

1 Before you read the chapter, respond to the statements

below on your worksheet or on a numbered sheet of paper

• Write an A if you agree with the statement.

• Write a D if you disagree with the statement.

2 After you read the chapter, look back to this page to see if

you’ve changed your mind about any of the statements

• If any of your answers changed, explain why

• Change any false statements into true statements

• Use your revised statements as a study guide

1 Air temperature is a weather factor

2 Air pressure does not affect weather

3 Clouds are made of water droplets or ice crystals

4 Weather conditions can change quickly

5 Excessive rainfall can lead to flooding

6 There is only one climate region in North America

7 Latitude affects the climate of an area

8 Ocean currents do not affect weather and climate

9 The area on the lee side (downwind slope) of a mountain experiences high rainfall

10 During the dry summers in California, the risk of fire increases

Before You Read

ing and connectin g, to help

you underst and com

parison s and con trasts.

Print a worksheet of

this page at

ca6.msscience.com

LESSON 1

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Figure 1 A weather report gives information about the weather factors for the day.

Identify the high and low temperatures for the day

468 Chapter 11 • Weather and Climate

>ˆ˜Ê`i> Weather describes the atmospheric conditions of

a place at a certain time

Real-World Reading Connection Weather affects our lives

in many ways—from the type of houses we build, to the way we dress, to the plans we make for activities each day How would you describe the weather where you live?

Weather Factors

Weather is the atmospheric conditions, along with short

term changes, of a certain place at a certain time If you have ever been caught in a rainstorm on what started out

as a sunny day, you know that weather conditions can change quickly—sometimes over just a few short hours

On the other hand, your area may have the same sunny weather for three days in a row before the weather changes.Perhaps the first things that come to mind when you think about weather are temperature and rainfall As you dress in the morning, knowing what the temperature will

be throughout the day helps you decide what to wear How would rain affect your plans?

Temperature and rainfall are just two of the factors used

to describe weather Barometric pressure, humidity, cloud coverage, visibility, and wind are other factors used to describe weather Examine the weather forecast shown in

Figure 1 for Los Angeles, California

Reading Guide

What You’ll Learn

factors used to describe

weather.

terms humidity, relative

humidity, and dew point.

that move water within the

water cycle.

Why It’s Important

Weather affects our lives in

relative to Earth’s surface

(p 401)

Science Content

Standards

4.a Students know the sun is the major

source of energy for phenomena on Earth’s

surface; it powers winds, ocean currents, and

the water cycle

4.e Students know differences in pressure,

heat, air movement, and humidity result in

changes in weather.

Lesson 1 • Weather 469

Air Temperature

The temperature of the air is a measure of

the average kinetic energy of air molecules

When the temperature is high, molecules

have a high kinetic energy Therefore,

mole-cules move faster than when temperatures are

cold Air temperatures change with time of

the day, season, location, and altitude

Air Pressure

Air pressure is the pressure that a column of

air exerts on the air below it Atmospheric

pressure decreases with height Therefore, air

pressure is higher close to Earth’s surface than

at higher altitudes Typical barometers, like the

one shown in Figure 2, measure air pressure in

millibars (mb) This pressure is referred to as

barometric pressure in a weather forecast

Knowing the barometric pressure of different

areas helps meteorologists predict the weather

What happens to air pressure as altitude increases?

Wind

Winds can change direction quickly

How-ever, many winds—such as the westerlies and

the trade winds—typically blow from the

same direction Traditionally, wind direction

is given as the direction from which the wind

is coming For example, the westerlies blow

from west to east The polar easterlies blow

from east to west Some local winds—called

northers—blow from the north.

Humidity

Water in the gas phase is called water vapor

The amount of water vapor present in air is

used to describe weather Humidity (hyew

MIH duh tee) is the amount of water vapor

per volume of air and is measured in grams of

water per cubic meter of air (g/m3) When the

humidity is high, there is more water vapor in

the air On a day with high humidity, your

skin might feel sticky and sweat might not

evaporate from your skin as quickly

ACADEMIC VOCABULARY

traditionally (tra DIH shuh nuh lee)

(adv) an established or

cus-tomary pattern or way of doing something

Traditionally, final exams are held during the last week of school.

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Figure 2 Air pressure is the sure that a column of air puts on the air below it A barometer measures air pressure

to drip from the sponge The amount of water vapor present in the air relative to,

or compared to, the maximum amount of water vapor the air can hold at that tem-perature before becoming saturated is the

relative humidity.

Relative humidity is given in percent For example, a relative humidity of 50 percent means that the amount of water vapor in the air is one-half of the maximum the air can hold at that temperature When weather forecasters give information about the humidity levels, they are usually refer-ring to relative humidity

Dew Point

Think about what happens when you leave a glass containing cold water on a table on a hot summer day Soon, water droplets begin to form on the outside of the glass The temperature at which air becomes fully saturated with water vapor

and condensation forms is the dew point.

When the air temperature drops, the air can hold less water vapor The water vapor

in air will condense to a liquid—dew, if the temperature is above freezing—or form ice crystals—frost, if the temperature is below 0°C The graph in Figure 3 shows the total amount of water vapor that can be held by air at different temperatures When the dew point is reached, the relative humidity

is 100 percent

When will dew form?

Use Figure 3 to determine whether dew

will form as the temperature changes

Data Collection

1 The relative humidity on a summer day is

80 percent The temperature is 35°C You

want to find out if the dew point will be

reached if the temperature falls to 25°C

later that evening Use Figure 3 to find

the amount of water vapor needed for

saturation at each temperature.

2 Calculate the amount of water vapor in

air that is 35°C at 80 percent relative

humidity (Hint: Multiply the amount of

water vapor air can hold at 35°C by the

percent of relative humidity.)

3 At 25°C, air can hold 22 g/m 3 of water

vapor If your answer from step 2 is less

than 22 g/m 3 , the dew point is not

reached and dew will not form If the

number is greater, then dew will form.

Data Analysis

the temperature drops from 35°C to

25°C at 80 percent humidity?

2 Predict During the day, the relative

humidity is 75 percent and the air

tem-perature is 5°C At night, the

tempera-ture falls to 0°C What will happen?

Figure 3 The graph shows that as air temperature increases, more water vapor can

be present in the air

Figure 4 Stratus clouds are flat, wide,

“layered” clouds and can be found at all altitudes Cumulus clouds are fluffy,

“heaped,” or piled-up clouds and can be found at all altitudes Cirrus clouds are

“wispy,” high-altitude clouds.

Figure 5 Fog is a surface cloud When you are in fog, you’re inside

a cloud.

Clouds and Fog

When air reaches its dew point, water vapor condenses to

form droplets These small droplets can come together to

form larger droplets that form clouds Clouds are water

drop-lets or ice crystals suspended in the atmosphere Clouds can

have different shapes and be present at different altitudes

within the atmosphere Pictures of different types of clouds

are shown in Figure 4 Since clouds move, they can transport

water and heat from one location to another Recall that

clouds are also important in reflecting some of the Sun’s

incoming radiation

When clouds form close to Earth’s surface, it is called fog

Fog is a suspension of water droplets or ice crystals close to

Earth’s surface Dense fog surrounding the Golden Gate

Bridge in San Francisco is shown in Figure 5 Fog reduces

visibility, which is the distance a person can see into the

atmosphere

How does fog form?

When you exhale air that is warmer than surrounding

out-side air on a cold winter day, the warm air cools down If the

dew point is reached, you can see the condensed water vapor

in a foggy cloud in front of your face

When water, in liquid or solid form, falls from the

atmo-sphere it is called precipitation (prih sih puh TAY shun)

Examples of precipitation—rain, snow, sleet, and hail—are shown in Figure 6 Rain is precipitation that reaches Earth’s surface as droplets of water Snow is precipitation that reaches Earth’s surface as solid, frozen crystals of water Sleet reaches Earth’s surface as small ice particles that began as rain in clouds, then froze as they passed through a layer of below-freezing air Hail reaches Earth’s surface as large pellets of ice Hail is formed when layers of ice are formed around a small piece of ice that is repeatedly caught in an updraft within a cloud

What is the difference between snow and sleet?

The Water Cycle

Water is essential for all living organisms Approximately 96 percent of Earth’s water is stored in the oceans Fresh water, present in glaciers, polar ice, lakes, rivers, and under the ground, represents only 4 percent of the water on Earth The

hydrosphere is the term used to describe all the water at Earth’s

surface Water constantly moves between the hydrosphere and

the atmosphere through the water cycle, which is shown in

Figure 7

Figure 7 What happens to water that reaches Earth’s surface as rain?

The Sun’s Energy

Ultimately, it is the Sun’s energy that drives the water cycle Solar radiation that reaches Earth’s surface causes water in the hydrosphere to change from a liquid to a gas, a process called evaporation Water that evaporates from lakes, streams, and oceans enters Earth’s atmosphere as water vapor As land and water are heated by the Sun, the air masses over them become warm and rise As the air masses rise, the air expands and cools down When the air cools down, the water vapor changes from a gas back into a liquid, a process called condensation As the water vapor condenses, water droplets form These water droplets then form clouds When the drop-lets become larger and heavier, precipitation falls from the clouds to Earth’s surface, returning water to the hydrosphere

What happens as the Sun’s heat warms Earth’s surface?

Figure 6 Rain, snow,

sleet, and hail are

Visualizing the Water Cycle

Lesson 1 • Weather 473

Figure 7

As the diagram below shows, energy for the

water cycle is provided by the Sun Water

continuously cycles between oceans, land,

and the atmosphere through the processes

of evaporation, transpiration, condensation,

and precipitation.

▲ Droplets inside clouds join to form bigger drops When the droplets become heavy enough, they fall as rain, snow, or some other form of precipitation.

Rain runs off the land into streams and rivers Water flows into lakes and oceans Some water is taken up by plants.

▲ Water evaporates from oceans,

lakes, and rivers Plants release water

vapor through transpiration.

▲ As it rises into the air, water vapor cools and condenses into water again Millions

of tiny water droplets form a cloud.

Contributed by National Geographic

LESSON 1 Review

474 Chapter 11 • Weather and Climate

Describing Weather and the Water Cycle

Temperature, precipitation, air pressure, and wind are some

of the factors that are used to describe weather The amount of water vapor in the air, or humidity, is also an important factor that determines the weather

Weather, along with the water cycle, is ultimately driven by the Sun’s energy As water moves between the hydrosphere and the atmosphere, water evaporates at Earth’s surface, clouds form, precipitation falls, and water returns to Earth’s surface

Science nline

For more practice, visit Standards Check at .

Summarize

Create your own lesson

summary as you write a

newsletter

1 Write this lesson title,

number, and page

num-bers at the top of a sheet

of paper

2 Review the text after

the red main headings

and write one sentence

about each These will be

the headlines of your

newsletter

3 Review the text and write

2–3 sentences about each

blue subheading These

sentences should tell who,

what, when, where, and

why information about

each headline.

4 Illustrate your newsletter

with diagrams of

impor-tant structures and

pro-cesses next to each

1 Distinguish between humidity

and relative humidity 4.e

2 In your own words, write the

definition for weather 4.e

Understanding Main Ideas

3 Which describes the process

by which water vapor changes from a gas into a liquid?

impor-5 Explain the difference between humidity and relative

9 Assess Explain how wind direction is used when nam- ing winds What are some advantages to using this system to name winds? 4.e

10 Organize Copy and fill in the graphic organizer below

In each oval, list the different types of precipitation 4.e

ELA6: W 1.2

Precipitation

LESSON 2

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Figure 8 When air masses travel, they transport heat and water vapor, which can affect local weather

>ˆ˜Ê`i> Several factors drive changes in weather

Real-World Reading Connection Weather can change quickly You might be enjoying a nice summer day when suddenly a cold breeze starts The temperature starts decreasing, and maybe it starts to rain

The Changing Weather

Weather conditions can change rapidly Why does this happen? How is weather affected by the movements of air masses and pressure changes?

Air Masses

An air mass is a body of air that has consistent features,

such as temperature and relative humidity Air masses get their characteristics from the surface over which they develop For example, an air mass that forms over a warm dry area will have warm dry conditions Figure 8 shows six major air masses that affect weather in the United States

Reading Guide

What You’ll Learn

factors involved in weather

weather events and their

effects.

Why It’s Important

Weather can change quickly

and can be severe

2.d Students know earthquakes, volcanic

eruptions, landslides, and floods change

human and wildlife habitats.

4.e Students know differences in pressure,

heat, air movement, and humidity result in

changes in weather.

[Insert Figure 9 - cold front and warm front]

Figure 9 A cold front

can move quickly

Thun-derstorms often form as

warm air is suddenly

lifted up over cold air

Warm air slides over

colder air along a warm

front This can lead to

hours, if not days, of wet

weather.

Describe the differences

between a cold front and a

occurs when a colder air mass moves toward warmer air The cold air pushes the warm air up into the atmosphere The warm air cools as it rises and water vapor condenses Clouds form and precipitation begins to fall In many cases, cold fronts give rise to severe storms

A warm front forms when lighter, warmer air moves over

heavier, colder air, as shown in Figure 9 Clouds form as the water in warm air condenses A warm front usually results in steady rain for several days

Highs and Lows

Have you ever heard a meteorologist using the terms pressure system and high-pressure system? Recall that when

low-warm air rises, it creates a decrease in pressure close to Earth’s surface Therefore an area of low pressure is created Areas of low pressure are associated with cloudy, stormy weather

What happens when cold air sinks? When cold air sinks,

it moves closer to Earth’s surface The surface air pressure increases as air moves down, and an area of high pressure is created This is referred to as a high-pressure system The sinking motion in high-pressure systems makes it hard for air

to rise and for clouds to form High-pressure systems are associated with fair weather

Why are high pressure systems associated with fair weather?

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Figure 10 Highs, lows, and fronts

help meteorologists forecast the

weather.

Predict What will the weather be like in

San Diego, California, for the next few days?

Lesson 2 • Weather Patterns 477

Weather Maps

Information on weather factors, high-

and low-pressure systems, and weather

fronts is usually represented in maps

These maps, called weather maps, provide

useful information on the atmospheric

conditions over areas of interest Weather

maps contain a lot of information that is in

the form of symbols A key for each symbol

is usually provided next to the map Study

the weather map shown in Figure 10 The

map contains information about pressure

systems and weather fronts for the western

United States Notice the symbols for high-

and low-pressure systems, cold fronts, and

warm fronts shown in the map legend

How do you interpret a satellite image?

Satellite images show the pattern of clouds and weather systems across a large region What can you learn about the weather from satellite images?

Procedure

1 Examine the satellite photo shown above

2 Identify the colors that represent clouds, ocean water, and land

3 Identify the United States and the Great Lakes on the map.

4 Identify the regions of the United States that have cloud cover Identify regions that have clear skies

Analysis

United States is there most likely a high-pressure system, according to the image? How do you know?

2 Infer Which region of the map is most

likely experiencing a low-pressure tem? Explain how you know this

sys-3 Explain why satellite images are helpful

to weather forecasters

4.e

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Figure 11 The amount

of solar radiation

reach-ing most of Earth’s

surface changes as Earth

completes its revolution

around the Sun

Identify What season is it

in the southern hemisphere

when it is summer in the

northern hemisphere?

478 Chapter 11 • Weather and Climate

Cycles that Affect Weather

Some of the cycles that regularly affect the weather include the day and night cycle, the seasons, and El Niño

Day and Night Cycles

Air goes through a daily cycle of warming and cooling As the Sun rises in the morning, sunlight warms the ground The ground warms the air by conduction until a few hours past noon As the Sun lowers in the afternoon, its energy is spread over a larger area Sometime in late afternoon or early evening, the ground and air above begin to lose energy and start to cool By late night or early morning, the coldest air is found next to the ground

Seasons

The regular changes in temperature and length of day that

result from the tilt of Earth’s axis are seasons Changes in the

amount of solar radiation received at different latitudes ing different times of the year give rise to the seasons

dur-Earth revolves around the Sun, as shown in Figure 11 As a result of Earth’s tilt on its axis, the amount of solar radiation reaching different areas of Earth changes as Earth completes its yearly revolution around the Sun More solar radiation reaches the northern hemisphere in June, when summer begins However, less solar radiation reaches the southern hemisphere during this same month, when winter begins During January, less solar radiation reaches the northern hemisphere, resulting in winter In the southern hemisphere, summer begins in January

What causes seasons on Earth?

WORD ORIGIN

season

from Latin sationem;

means a sowing

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Figure 12 Both northern hemisphere jet streams shift northward during an El Niño In the United States, this often leads to warmer-than- usual temperatures in the north and increased rain and flooding in the south The home shown above slipped down a hillside eroded by heavy

El Niño rains.

Lesson 2 • Weather Patterns 479

El Niño and La Niña

El Niño and La Niña can affect weather worldwide During

an El Niño period, warmer surface water in areas of the

eastern equatorial Pacific Ocean leads to more water vapor

being in the air above the water This can result in increased

rainfall across the southeastern United States, and the South

American countries of Peru and Ecuador Heavy rainfall

can lead to flooding and landslides like the one shown in

Figure 12 On the other side of the globe, severe droughts can

occur in Australia, Indonesia, and southeast Africa In many

cases, the droughts lead to forest fires as well During El Niño

years, the north-central United States sometimes experiences a

milder-than-normal winter The Carribean and southeastern

United States experience a decrease in the number of

hurricanes

A La Niña event occurs when sea surface temperatures in the

eastern equatorial Pacific are colder than normal This can

produce colder-than-normal winter temperatures in the

north-western United States It also leads to warmer-than-normal

winter temperatures in the southeastern United States

Figure 12 shows how El Niño affects the location of the polar

and subpolar jetstreams over the United States

480 Chapter 11 • Weather and Climate

Severe Weather

Sometimes weather can be severe and cause hazardous conditions For example, extensive rainfall can lead to floods Other times, rainfall can be absent for long periods of time These events can pose a threat to all living things in the affected area, including humans, animals, and plants

Droughts

A period of time when precipitation is much lower than

normal or absent is a drought Droughts can last months or

years Droughts can bring about several hazardous conditions for ecosystems and human populations If an extended

drought occurs in a region where precipitation is normally low, there can be a major decrease in water supply for the population of that region A decrease in water supply also affects agriculture and, in extreme cases, can result in famine.California experienced significant droughts from 1987 until the beginning of 1993 These droughts lasted a relatively long time and resulted in a decrease in the region’s water res-ervoirs Although the droughts in California were significant,

they did not have the same severe consequences as droughts

that occurred in areas of Africa, where thousands of lives were lost The photos in Figure 13 show lowered water levels and fires caused by the extreme dryness of a drought

Why is a drought an example of severe weather?

ACADEMIC VOCABULARY

consequence

(KAHN seh kwents)

(noun) something produced

by a cause

One consequence of increased

rainfall could be flash floods.

Figure 13 Don Pedro Reservoir, east of Modesto, is the sixth-largest body of

water in California In 2003, drought lowered its water level, as shown in the

photo on the left Also in 2003, drought intensified a fire storm, shown on the

right, as it descended from the foothills at night toward East Highlands, near

San Bernardino, California.

Figure 14 These utility workers are patrolling a California suburb tem- porarily deserted after flooding caused by El Niño.

Lesson 2 • Weather Patterns 481

Floods

Sometimes, when severe weather occurs, it leads to

flood-ing Floods occur when water enters an area faster than it can

be taken away by rivers, absorbed by the ground, or

con-tained in lakes Floods can occur when periods of extended

heavy rain or melting snow increase the amount of water in

rivers, producing an overflow Flooding also can occur when

snow melts rapidly, producing large amounts of runoff When

soils cannot retain water well, flooding can also happen As

shown in Figure 14, floods can damage, wash away, or even

bury the living areas of both humans and wildlife

Floods are common natural disasters and can occur in

many locations For example, in 1993, an enormous flood

took place in the Midwest region of the United States This

flood has been one of the most damaging floods in the

United States In 1997, several floods took place in different

locations of the United States, including California More

recently, New Orleans was almost completely destroyed by

the flood waters that poured into the city from Hurricane

Katrina in August 2005

A flash flood is a flood that takes place suddenly Flash

floods, like the one shown in Figure 15, are the most

danger-ous type of floods With deaths at over 200 people per year,

flash floods are the number-one reason for weather-related

deaths in the United States Unfortunately, the damaging

effect of flash floods is increasing due to human activities

This is because the construction of buildings, parking lots,

and other structures decreases the amount of vegetation and

soil that can potentially absorb runoffs of water

Figure 15 Heavy rain in northern California caused the Russian River to rise 3 meters above flood stage in early January, 2006 Flash floods and mudslides killed at least

14 people and forced thousands to flee their homes.

Science nline

For more practice, visit Standards Check at .

Summarize

Create your own lesson

summary as you design a

visual aid.

1 Write the lesson title,

number, and page

num-bers at the top of your

poster

2 Scan the lesson to find

the red main headings

Organize these headings

on your poster, leaving

space between each.

3 Design an information

box beneath each red

heading In the box, list

2–3 details, key terms,

and definitions from each

1 The regular changes in

tem-perature and length of day that result from the tilt of Earth’s axis are

4.e

2 A is a period

of time when precipitation is much lower than normal 4.e

Understanding Main Ideas

3 What kind of weather usually

results from a warm front? 4.e

A steady rain for several days

B a severe storm

C clear, sunny sky

D clouds but no rain

4 List some of the factors that can cause changes in weather.

Pressure System

Low High

ELA6: R 2.4

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Real-World Reading Connection Think about the climate

of your area How does your winter differ from that of Minneapolis, Minnesota, where the average temperature in January is –11°C?

A World of Many Climates

We live in a world of different climates—from hot and dry desert areas, to warm and wet rainforest regions, to frigid cold tundra at the poles The climate present in dif-ferent regions affects all of the organisms living there

What is climate?

The long-term average of the weather patterns of an area

is climate This includes temperature, winds, and

precipi-tation over a long period of time Often, climate data is presented in graphs like the ones in Figure 16

those of a highland climate.

influence the climate of a

region.

in which human activities

can affect the climate.

Why It’s Important

Like weather, climate

influences all living things in

4.d Students know convection currents

distribute heat in the atmosphere and oceans

4.e Students know differences in pressure,

heat, air movement, and humidity result in

changes in weather.

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Figure 17 North

America has many

different climate regions

Most of California has

shows the climate regions of North America As shown in

Figure 17, most of California has mediterranean and highland

climates A mediterranean (me dih tur RAY nee en)

climate is characterized by mild, wet winters and hot, dry

summers Mediterranean climates usually occur on the ern side of a continent Summer fires, due to dry conditions, often occur in a mediterranean climate

west-A highland climate is characterized by cool-to-cold

tem-peratures and occurs in the mountains and on high plateaus Recall that as altitude increases, the temperature decreases

In California, the influence of altitude on climate can be easily observed On a sunny winter day, a person can be in Newport Beach, California, and observe the peaks of the nearby mountains covered in snow, such as Big Bear

Although the latitude of the two locations, Newport Beach and Big Bear, are nearly the same, differences in altitude cause a large difference in temperature

Figure 17 Which regions of North America have a dry climate?

WORD ORIGIN

climate

from Latin clima;

means region, slope of Earth

Figure 18 Higher latitudes receive less solar

radiation and have lower average temperatures

As latitude decreases, average temperatures

increase

3TEP 3TEP

Earth’s climates are shaped by energy

received from the Sun Uneven heating of

Earth’s surface results in air and ocean

currents that influence the different

cli-mate regions Other factors, such as

latitude and altitude, the distance from a

large body of water, and mountain barriers,

also affect climate These factors are called

climate controls Some of these factors,

such as latitude and mountain barriers, are

unchanging Other factors, such as winds

and ocean currents, can vary over the

course of a year

Latitude

Recall that areas close to the equator

receive more solar radiation per unit of

surface than areas located further north

or south Since more solar radiation is

received in areas near the equator, these

areas have warmer climates than regions

at higher latitudes The farther a region is

from the equator, the colder its climate

The graph in Figure 18 shows how air

temperature changes with latitude

How does latitude affect the angle of sunlight?

Investigate to see how different latitudes affect the angle at which the Sun’s rays strike Earth.

Procedure

1 Complete a lab safety form.

2 Place a globe on a table or desktop

3 Hold a flashlight parallel to the floor

and aim the beam of light directly at the equator on the globe Record your observations about how the beam hits the globe

4 Keep the flashlight parallel to the floor Aim the beam between 35–40° N latitude Record your observations about how the beam hits the globe

5 With the flashlight parallel to the floor, aim the beam between 35–40° S latitude Record your observations about how the beam hits the globe

6 Find the state of California on the globe

Analysis

observe as the light beams hit the globe

at the different latitudes?

2 Infer How would the differences you

observed affect the climate of the different regions?

3 Describe Where is California compared

to the latitudes at which light was aimed?

4.d

Figure 19 Large bodies of water,

such as oceans, tend to modify climate

by preventing the more extreme

temperature changes that can occur in

inland areas.

486 Chapter 11 • Weather and Climate

Distribution of Land and Water

The distribution of land and water has an important ence on climate Recall that water can absorb or lose large amounts of thermal energy with little change in temperature Land does not have this characteristic Land surfaces heat and cool rapidly Ocean surfaces heat and cool slowly As a result,

influ-the climate of locations near an ocean is affected As shown

in Figure 19, the average daytime temperature in southern California generally increases as one moves east from coastal areas to nearby inland areas At night, temperatures along the coast are usually higher than inland

Ocean Currents

Ocean currents help to redistribute the Sun’s energy on Earth in the form of heat Ocean currents that move water away from the equator, such as the Gulf Stream, carry heat to higher latitudes Currents moving toward lower latitudes, such as the California Current, replace warm water from the lower latitudes with cold water from higher latitudes

This redistribution of heat can be seen when comparing the average winter temperatures of Great Britain to those of Labrador, Canada These two locations are found at the same latitude However, due to the warm-water influence of the Gulf Stream, the average winter temperature in Great Britain

is 15–20°C warmer than that of Labrador

The California Current, is a cold-water current that flows past the coast of California The water temperature of the California current remains stable year-round This helps keep temperatures along the coast from rising too high in the summer and from dipping too low in the winter

How do ocean currents influence climate?

ACADEMIC VOCABULARY

affect (ah FEKT)

(verb) to produce an effect

The weather along the coast of

California is affected by the

California current.