chapter: weather and climate

Chapter: Weather and Climate

Table of Contents

Section 2: Weather

Section 1: Earth’s Atmosphere

Section 3: Climate

Section 4: Earth’s Changing Climates

• Air is a mixture of gases. Nitrogen is the largest component with 78 percent and oxygen is next with 21 percent by volume. Most of the remaining one percent is the inactive gas argon and water vapor.

• The remaining portion is a mixture of trace gases, so called because they are present in such small, barely detectable amounts.

Atmospheric CompositionEarth’s Atmosphere

1

• Cellular respiration by organisms produces water vapor and carbon dioxide (CO2).

• Photosynthetic organisms use carbon dioxide and produce almost all the oxygen in the atmosphere.

Biological ProcessesEarth’s Atmosphere

1

• Microorganisms in swamps, rice paddies, and soil produce nitrogen and methane.

• The microorganisms in the digestive tracts of animals such as termites, cows, and sheep produce methane.

Biological ProcessesEarth’s Atmosphere

1

• Earth’s early atmosphere contained mostly hydrogen and helium.

• These gases were lost and were replaced by gases from volcanic eruptions.

Formation of the AtmosphereEarth’s Atmosphere

1

• Oxygen from photosynthetic marine organisms accumulated in the atmosphere and intense solar radiation converted some of it into ozone.

• Earth’s atmosphere extends more than 1,000 km above earth’s surface.

• Most of our weather takes place within the troposphere, a layer extending 30 km above Earth’s surface.

Atmospheric StructureEarth’s Atmosphere

1

• In this layer temperature normally decreases with height.

• Sometimes, however, temperature increases with height. This is called a temperature inversion.

• Above the troposphere is the stratosphere, which is extremely dry and rich in ozone.

• Here, temperature always increases with height, creating a permanent temperature inversion.


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1

• The place where this temperature inversion begins is called the tropopause.

• The energy that heats the atmosphere ultimately comes from the Sun.

• Ozone absorbs nearly all of the sun’s ultraviolet radiation.

Heating the AtmosphereEarth’s Atmosphere

1

• As Earth’s surface is heated, it emits long-wave, infrared radiation.

• Trace gases, such as carbon dioxide and water vapor, absorb long wavelengths and re-emit some of them back to Earth’s surface.


1

• The term greenhouse effect refers to this re-emission of infrared radiation back to Earth’s surface.

• Latent heat is heat energy released or absorbed during the phase changes of water, such as evaporating water or melting snow.


1

• Cloud formation is the first step in the precipitation process.

Water in the AtmosphereEarth’s Atmosphere

1

• Cumulus clouds form from rising air parcels.• Stratus-type clouds form mainly when layers

of air rise gently.

Water in the AtmosphereEarth’s Atmosphere

1

• For precipitation to occur, droplets must grow large.

• Growth can occur when droplets collide and combine.

Global Water CycleEarth’s Atmosphere

1

• Precipitation, runoff, storage, and evaporation make up the global water cycle.

Section Check

1Question 1

Air can be described as a _______.

A. combination of elementsB. compoundC. mixtureD. solution

Section Check

1Answer

The answer is C. Air is a mixture of gases; including nitrogen, oxygen, and water vapor.

Section Check

1Question 2

Temperature _______ with height in the troposphere.

A. decreasesB. doublesC. increasesD. stays the same

1Section Check

AnswerThe answer is A, decreases.

Section Check

1Question 3

Which cloud type is an example of a low cloud?

A. altostratusB. cirrocumulusC. cirrostratusD. cumulus

1Section Check

Answer

The answer is D. Cumulus clouds form from rising air parcels. If they produce rain, it is usually only brief showers.

Weather

2

• Weather patterns result from complex global patterns of wind and pressure.

Atmospheric Pressure

• The most important of these are the westerlies—winds that blow from the west in the middle latitudes—and the trade winds, which blow from the east, in the tropics.

Global Winds and Pressure Systems

Weather

2

• Two factors produce these global patterns—unequal heating between the equator and poles and the rotation of Earth.

Global Winds and Pressure Systems

Weather

2 Global Winds and Pressure Systems• Imbedded in these wind systems are fast and

powerful jet streams.

Weather

2

• Subtropical highs are relatively stable belts of high pressure near latitudes of 30°.

High and Low Pressure Systems

• Sub-polar lows and the westerlies tend to meander as smaller cells of high and low pressure develop.

• The lows generally develop from a disturbance in the polar front jet and move eastward with the jet stream.

Weather

2

• Air masses can be polar or tropical and continental or maritime.

Air Masses and Weather Fronts

• Air masses interact in zones called weather fronts.

• Warm and cold fronts create different types of precipitation.

Weather

2

Weather

2

• A typical cumulonimbus cloud has ice crystals near its top.

Severe–WeatherThunderstorms

Weather

2 Severe–Weather

• Sometimes these ice crystals act as nuclei to trigger further growth of cloud droplets.

• This forms hail.

Thunderstorms

Weather

2

• The force of the falling precipitation in a thunderstorm may pull with it cold air bursts from higher in the cloud.

Downdrafts and Squalls

• This sinking current of cold air is called a downdraft.

• When a downdraft hits the surface with particularly strong force, it spreads out in a series of windy gusts called squalls.

Weather

2

• Cold air descends from a thunderstorm and hits the ground.

Downbursts

• When it hits the ground, it bursts outward like the spokes on a wheel.

Weather

2

• Tornadoes are intense, short-lived localized storms in the mid-latitudes.

Tornadoes and Hurricanes

• This map shows where tornadoes frequently occur.

Weather

2 Tornadoes and Hurricanes• A twisting, funnel-shaped tornado cloud can

move across land at a speed of around 50 km/h.

• Intense, circular winds in the funnel can reach speeds up to 400 km/h.

Weather

2

• Hurricanes are tropical storms that cover vast areas and last for days.

Tornadoes and Hurricanes

• When winds exceed 118 km/h, the storms are called hurricanes.

2Question 1

What causes the atmospheric pressure on your body?

A. air pocketsB. gas molecules moving and collidingC. gravityD. Earth’s rotation

Section Check

2Answer

The answer is B. The number of air molecules decreases as altitude increases so pressure always decreases with altitude.

Section Check

2Question 2

Which produces showers and thunderstorms?

A. cold frontB. occluded frontC. stationary frontD. warm front

Section Check

2Answer

The answer is A. In a cold front, air pushes the warm air aloft in a random and chaotic fashion, forming cumulus clouds.

Section Check

2Question 3

Where would you be least likely to experience a tornado?

A. KansasB. New YorkC. OklahomaD. Texas

Section Check

2Answer

The answer is B. Tornadoes are more common in the Great Plains, lower Midwest, and parts of the south.

Section Check

Climate and Weather• Climate means the long-term average of

weather conditions—wind, temperature, precipitation, moisture, and other aspects of weather.

Climate

3

Climate System

• This biogeophysical system can be visualized as five spheres that interact to create the environments in which we live.

Climate

3

Climate System

Climate

3

• The biosphere is everything organic.• The hydrosphere is

liquid water.• The cryosphere is

frozen water in snow, ice, and glaciers.

• The lithosphere is the solid Earth.

What causes climate?

Climate

3

• Latitude is the primary factor that determines climate at a given location.

• The amount of radiation received from the Sun and the prevailing circulation features depend on latitude.

Causes of Mean Temperature

Climate

3

• In the winter, the amount of solar radiation varies, because of the low angle at which it strikes Earth.


Climate

3

• In summer, sunlight strikes at a higher angle and periods of daylight are longer.


Climate

3

• The strong temperature gradients in winter and spring help to create storms and severe weather.

Ocean and Land Influence

Climate

3

• Areas with little direct ocean influence are called continental climates and have steep temperature gradients.

• A climate with strong ocean influence is called a maritime climate.

Precipitation

Climate

3

• Wind and pressure patterns determine precipitation.

Influence of Mountains

Climate

3

• Mountains act as barriers in the wind, blocking weather systems and altering patterns of precipitation.

• When the wind blows perpendicular to one side of a mountain range, a lee rain shadow forms on the opposite side.

Influence of Water

Climate

3

• A sea breeze blows from the water toward the land in the afternoon, when the land is warmer than the water.

• Warm air rises over the land creating low pressure that allows cool, dense air to blow from the sea toward land.

• The reverse happens at night.

Types of Climates

Climate

3

• Climate classification has three major divisions— cold or boreal, arid and semi-arid, and climates with adequate heat and precipitation.

Types of Climates

Climate

3

• The last includes temperature, subtropical, and tropical climates.

Section Check

Question 1

Compare and contrast the atmosphere and the biosphere.

The atmosphere includes the air around us. The biosphere is everything organic, including plants, animals, and humans.

3

Answer

Section Check

Question 2

Which is the primary factor that determines the climate at a given location?

A. abiotic factorsB. biotic factorsC. latitudeD. longitude

3

Section Check

Answer

The answer is C, latitude.

3

Section Check

Question 3

What type of vegetation would you expect to see in a climate that is cold and dry?

3

A. boreal evergreen forestB. temperate woodlandC. grasslandD. tropical deciduous forest

Section Check

AnswerThe answer is A, boreal evergreen forest.

3

Seasonal Changes• Seasonal changes occur as Earth completes

a revolution around the Sun.

• The hemisphere tilted toward the Sun experiences summer while the hemisphere tilted away from the Sun experiences winter.

Earth’s Changing Climates

4

Long-term Changes• Cycles of glaciations, called ice ages,

represent long-term climatic change.

• The peak of the last ice age was 18,000-22,000 years ago when global was about 6°C cooler than present.


4

Long-term Changes• World climate

reached its current pattern only about 3,000 years ago.


4

Causes of Climate Change• Changes related to Earth’s orbit are the most

important factors, producing changes that determine the rhythmic cycles of glaciation.


4

• These include changes in the tilt of Earth’s axis of rotation, the shape of its orbit, and the timing of the seasons with respect to distance from the Sun.

The Human Factor• Human activities modify the surface heating

and the water and carbon cycles.


4

The Human Factor


4

• They also increase the atmospheric concentrations of trace gases, dust and air pollution.

The Human Factor• The carbon cycle is affected in two ways by

deforestation and loss of vegetation.


4

• Less carbon dioxide is absorbed from the atmosphere during photosynthesis.

• Decaying and burning wood adds carbon dioxide to the atmosphere.

The Human Factor


4

• Human activities have also increased the concentration of other trace gases—methane and nitrous oxide.

• All of these gases are important in heating the atmosphere.


4

• Global warming is an increase in the average global temperature of Earth.

• Synthetic chemical compounds could destroy atmospheric ozone.

The Human Factor

The Ozone Hole

• Exhaust from supersonic aircraft and chlorine and fluorine compounds, such as CFCs, are some compounds that could destroy atmospheric ozone.


4

• British scientists found a hole in the ozone layer over Antarctica.

• When study of the air in this hole showed that it was largely man-made, an international agreement was made to limit the use of CFCs.

The Ozone Hole


4

• El Niño is a climatic event that involves the atmosphere and oceans.

• El Niño can dramatically alter global weather patterns.

El Niño and La Niña

• The opposite of El Niño is La Niña, which occurs when tradewinds in the Pacific are unusually strong and equatorial oceanic surface temperatures are colder than normal.

Section Check

Question 1

How can volcanoes cause changes in climate?

Volcanoes expel vast amounts of dust that can block sunlight for years. If sunlight is blocked then a decrease in global temperatures could result.

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Answer

Section Check

Question 2

Which is NOT a way that humans have affected Earth’s atmosphere?

4

A. burning fossil fuelsB. deforestationC. draining of wetlandsD. reintroduction of threatened species

Section Check

Answer

The answer is D. All of the other choices have had an effect on Earth’s atmosphere.

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Section Check

Question 3

Where is the ozone hole the largest?

A. AntarcticaB. AustraliaC. North AmericaD. South America

4

Section Check

Answer

The answer is A. In 1985, British scientists found a hole in the ozone layer over Antarctica.

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