Chapter 17

The Atmosphere:

Structure and Temperature

Atmosphere Characteristics• Earth is the only planet in our universe with an

atmosphere that is able to sustain life.• The state of the atmosphere at a given time

and place is known as weather.• The combination of Earth’s motions and

energy from the sun produce a variety of weather.

• Climate is based on observations of weather that have been collected over many years.– Climate helps describe a place or region.

Question:

Which of the following is an example of climate?

A. A sudden snowstorm resulted in subzero temperatures and 30cm of new snow.

B. In southern California, temperatures are generally mild and rainfall is low.

C. Record-breaking low temperatures caused a sudden freeze one day in Des Moines.

D. A week of rain caused widespread flooding in Seattle.

Atmosphere CharacteristicsComposition of the Atmosphere• Major Components

– The atmosphere is a mixture of different gases and particles, each with their own physical properties, and it varies from place to place.

– If all the water vapor, dust, and other variable components were removed, its makeup would be very stable up to about 80 kilometers.

Atmosphere CharacteristicsComposition of the Atmosphere• Variable Components

– Important materials that vary in the air (water vapor, dust, ozone, etc.), have significant effects on weather and climate.

– The amount of water vapor varies from almost none to about 4% by volume.

– Water vapor is the source of all clouds and precipitation.

– It also absorbs heat given off by the Earth and absorbs some solar energy, therefore it plays a significant role in heating the atmosphere.

Atmosphere CharacteristicsComposition of the Atmosphere• Variable Components

– The dust particles include sea salts from breaking waves, fine soil blown into the air, smoke and soot from fires, pollen and microorganisms lifted by the wind, and ash and dust from volcanic eruptions.

– The ozone is a form of oxygen that combines three oxygen atoms into each molecule (O3).• Ozone is not the same as the oxygen we breathe.

– The ozone is what protects us from harmful ultraviolet radiation (UV) from the sun.• If ozone did not filter most UV radiation, our planet would be

uninhabitable for many living organisms.

Atmosphere Characteristics

Atmosphere CharacteristicsComposition of the Atmosphere• Human Influence

– Humans influence the atmosphere through pollutants (i.e. emissions from cars, factories, etc.)

– There are two different types of air pollutants:• Primary Pollutants: Emitted directly from identifiable

sources (i.e. cars, factories, etc.).• Secondary Pollutants: Not emitted directly into air (i.e.

acid rain, smog, etc.).– Secondary pollutants form in the atmosphere when reactions

take place between primary pollutants and other substances.» Acid Rain = Primary Pollutant SO2 reacts with Oxygen in air to

produce SO3, which then combines with water to produce sulfuric acid (H2SO4).

Atmosphere Characteristics

Question:

Most of Earth’s dry air is made up of

A. Carbon dioxide and oxygen.

B. Nitrogen and argon.

C. Nitrogen and oxygen.

D. Oxygen and argon.

Question:

What percentage of water vapor is found in the air?

A. 0-1 percent

B. 0-4 percent

C. 0-8 percent

D. 0-10 percent

Question:

How is ozone produced?

A. One molecule of oxygen is split into two atoms.

B. Two atoms of oxygen combine to form one oxygen molecule.

C. Two molecules of oxygen are split simultaneously into four atoms.

D. One atom of oxygen collides with the one molecule of oxygen.

Atmosphere CharacteristicsHeight and Structure of the Atmosphere• As the atmosphere gets higher and higher in

altitude it gets thinner and thinner, until there is no more atmosphere (space).

• Also as the atmosphere gets higher, the pressure drops (atmospheric pressure).– Atmospheric pressure at sea level = 14.6 psi.

• Also as the atmosphere gets higher, the temperature drops, but this trend is not the same in all the layers of the atmosphere.

Atmosphere Characteristics

Atmosphere CharacteristicsHeight and Structure of the Atmosphere• Temperature Changes

– The atmosphere can be divided vertically into four layers based on temperature.• Troposphere, Stratosphere, Mesosphere, ad Thermosphere.

– The troposphere is the bottom layer where all important weather phenomena occur.• On average the temperature drops as altitude rises in the

troposphere.

– In the stratosphere, the temperature remains constant to a height of 20 km, then it begins to increase in temperature until nearly 50 km.• The increase in temperature is due to the ozone being located in

this region, absorbing UV radiation.

Atmosphere CharacteristicsHeight and Structure of the Atmosphere• Temperature Changes

– The mesosphere is the layer of the atmosphere immediately above the stratosphere and is characterized by decreasing temperatures with height.

– The thermosphere is the region of the atmosphere immediately above the mesosphere and is characterized by increasing temperatures due to the absorption of very short-wave solar energy by oxygen.

Atmosphere Characteristics

• Snowy Mountaintops Contrast with Warmer Snow-Free Lowlands

Question:

In which level of the atmosphere is ozone concentrated?

A. Troposphere

B. Stratosphere

C. Mesosphere

D. thermosphere

Question:

In which layer of the atmosphere does our weather occur?

A. Thermosphere

B. Mesosphere

C. Stratosphere

D. Troposphere

Atmosphere CharacteristicsEarth-Sun Relationships• Nearly all of the energy that drives Earth’s

variable weather and climate comes from the sun.

• The amount of energy received varies with latitude, time of day, and season of the year.

• The variations in solar heating are caused by the motions of Earth relative to the sun and variations in Earth’s land and ocean surface.– Unequal heating of Earth results in wind and

drives the ocean currents.

Atmosphere CharacteristicsEarth-Sun Relationships• Earth has two principle motions:

– Rotation: Spinning about Earth’s axis.• 1 rotation of Earth takes 24 hours.

– Revolution: The movement of Earth in its orbit around the sun.• 1 revolution of Earth around the sun takes 1 year.

• Season changes occur because Earth’s position relative to the sun continually changes as it travels along its orbit.

• Earth is tilted at an angle of 23.5° from the perpendicular, therefore causing the change in seasons as we move around the sun.

Length of Daylight• The length of daylight compared to

the length of darkness also is determined by Earth’s position in orbit.

Atmosphere CharacteristicsSolstices & Equinoxes• The four seasons we experience on Earth are Fall,

Winter, Spring, and Summer.• There are four important dates to remember

(Northern Hemisphere):– June 21st or 22nd each year is known as the summer

solstice (first day of summer).– December 21st or 22nd each year is known as the winter

solstice (first day of winter).– September 22nd or 23rd each year is known as the

autumnal equinox (first day of fall).– March 21st or 22nd each year is known as the spring

equinox (first day of spring).

Question:

Seasonal changes occur because of

A. Earth’s tilt.

B. Earth’s shape.

C. The distance between Earth and the moon.

D. The time of year.