300 Earth's Atmosphere

Energy from the sun heats the Earth unevenly, causing air movements resulting in changing weather patterns. As a basis for understanding this concept, students know:

the Earth’s atmosphere exerts a pressure that decreases with distance above the Earth’s surface, and is the same in all directions.

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II. Goals of this module -

To learn the composition and structure of the Earth’s atmosphere.

To learn the cause of the seasons.

To learn the definitions of and proper spelling for scientific terms that are used commonly in newspapers, magazines, and books, and on television and radio programs in discussions about the Earth’s atmosphere.

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III. Composition of the Earth’s atmosphere -

Generally constant components of air -

Nitrogen - 78%

Oxygen - 21% - supports animal life on earth.

Argon - 0.93%

Carbon dioxide - 0.035% - supports plant life on earth; absorbs heat energy radiated by the earth.

Variable components -

Water vapor - 0% to 4% - provides rain; absorbs heat energy radiated by the earth and the sun.

Dust - controls the amount of sunlight that reaches the earth.

Ozone - absorbs ultraviolet radiation from the sun.

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IV. Height and structure of the atmosphere -

Half of all the atmosphere is below an altitude of 3.5 miles; 90% is below an altitude of 16 miles; almost all of the atmosphere is below an altitude of 60 miles.

Temperature boundaries -

Troposphere - all important weather phenomena occur here; temperature decreases about 3.5¡F/1,000 feet (lapse rate) because air density decreases with altitude, hence particle collisions are less frequent and heat generation is less.

Tropopause - at about 7 miles altitude; temperature is constant with increase in altitude.

Stratosphere - ozone occurs here; ozone absorbs ultraviolet radiation and causes a temperature increase (inversion) in this zone.

Stratopause - at about 30 miles altitude; temperature is constant with increase in altitude.

Mesosphere - temperature decreases in this zone because of air density decrease with altitude as in the troposphere.

Mesopause - at about 50 miles altitude; temperature is constant with increase in altitude.

Thermosphere - absorption of very short-wave solar radiation causes a temperature increase in this zone.

DIAGRAM OF EARTH’S ATMOSPHERE

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V. Factors determining the heat energy received from the sun

Inclination of the sun - equal amounts of heat energy are spread over a wider area as the sun's inclination decreases; half as much at 30¡ as at 90¡.

Thickness of the atmosphere penetrated - the lower the inclination of the sun, the greater will be the thickness of the atmosphere penetrated, and the more heat energy will be absorbed by the water vapor in the atmosphere.

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VI. Summer and winter seasons -

DIAGRAMS OF THE SOLSTICES

June solstice -

North pole tilted 23.5¡ directly toward sun

Sun directly over the Tropic of Cancer (23.5¡N latitude)

24 hours daylight north of Arctic Circle (66.5¡N latitude)

24 hours darkness south of Antarctic Circle (66.5¡S latitude)

Beginning of summer in northern hemisphere

Beginning of winter in southern hemisphere

December solstice -

South pole tilted 23.5¡ directly toward sun

Sun directly over the Tropic of Capricorn (23.5¡S latitude)

24 hours darkness north of Arctic Circle (66.5¡N latitude)

24 hours daylight south of Antarctic Circle (66.5¡S latitude)

Beginning of winter in northern hemisphere

Beginning of summer in southern hemisphere

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VII. Spring and autumn seasons -

March equinox -

Earth's axis is perpendicular to the sun

Sun is directly over the Equator (0¡ latitude)

Entire earth receives 12 hours each of daylight and darkness

Beginning of spring in the northern hemisphere

Beginning of autumn in the southern hemisphere

September equinox -

Earth's axis is perpendicular to the sun
Sun is directly over the Equator (0¡ latitude)
Entire earth receives 12 hours each of daylight and darkness
Beginning of autumn in the northern hemisphere
Beginning of spring in the southern hemisphere

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VIII. Three paths taken by radiation -

Reflected - path of waves is redirected by bouncing off of particles of matter, such that the angle of incidence is equal and opposite to the angle of reflection. Ability of a substance to reflect energy is referred to as its albedo. (25% of solar radiation is reflected back to space.)

Scattered - path of waves is redirected by bouncing off of particles of matter in any direction other than reflection. (5% of solar radiation is scattered back to space.)

Absorbed - waves are trapped inside of molecules and the energy is transformed into increased molecular motion which is measured by an increase in temperature. (70% of solar radiation is absorbed by earth and atmosphere.)

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IX. The "Greenhouse Effect" and "Global Warming" -

Energy coming from the sun is short wavelength energy and in the atmosphere only oxygen, ozone, and water vapor absorb much of it, mostly the ultraviolet portion. (20% of solar radiation is absorbed by the atmosphere. 50% of solar radiation is absorbed by the Earth.)

Radiation absorbed by the earth is radiated back toward space as long wavelength energy which is absorbed by water vapor and carbon dioxide in the atmosphere at a much greater rate than solar radiation is absorbed. The result is that heat is trapped in the troposphere to produce a "greenhouse effect".

Increase in atmospheric carbon dioxide since the industrial revolution produces more absorption and "global warming".

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X. Controls of temperature -

Latitude - low angle of inclination of the sun at high latitudes produces a relatively greater thickness of atmosphere to be penetrated, so more solar radiation is absorbed by the atmosphere and the earth receives less solar radiation. (Temperature decreases with distance from the equator.)

Altitude - more earth radiation is absorbed by the atmosphere at lower altitudes than at higher altitudes. (Temperature decreases with increase in altitude.)

Land and water - land absorbs solar radiation better than water and the heat produced from radiation absorbed by water is mixed and cooled. (Temperature increases with distance from water.)

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XI. Laboratory exercises -

MAKE A DIAGRAM OF THE SEASONS -

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XII. Possible essay questions -

List the seven major components of the atmosphere along with the relative abundances of those components that are generally constant.

Describe and illustrate the various zones that are recognized in the atmosphere.

Explain and illustrate how the inclination of the sun and the thickness of the atmosphere effect the energy received from the sun.

Describe and illustrate the relative positions of the Earth and sun during the June and December soltices and explain the day versus night relationships that exist at those times.

Describe and illustrate the relative positions of the Earth and sun during the March and September equinoxes and explain the day versus night relationships that exist at those times.

Describe the cause of the "greenhouse effect" and "global warming".

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XIII. Practice Questions

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