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Chapter 14Chapter 14

Composition, Structure,




A. Weather

1. Weather measured over a short period of time

2. Constantly changing


B. Climate

1. Climate measured over a long period of time

2. Generalized, composite of weather


C. Elements of weather and climate

1. Properties that are measured regularly

2. Most important elements

a. Temperature

b. Humidity

c. Cloudiness

d. Precipitation

e. Air pressure

f. Wind speed and direction

A. Air is a mixture of discrete gases

B. Major components of clean, dry air

1. Nitrogen ( N )-- 78 %

2. Oxygen ( O ) -- 21 %

3. Argon and other gases

4. Carbon dioxide ( CO 2 ) -- 0.035 % -- absorbs heat energy from Earth


C. Variable components of air

1. Water vapor

a. Up to about 4 % of the air’s volume

b. Forms clouds and precipitation

c. Absorbs heat energy from Earth

2. Dust

a. Includes pollen and spores

b. Water vapor condenses on

c. Reflects sunlight

d. Helps color sunrise and sunset


3. Ozone

a. Three-atom oxygen ( O 3 )

b. Distribution not uniform

c. Concentrated between 10 to 50 kilometers above the surface

d. Absorbs harmful UV radiation

e. Human activity is depleting ozone by adding chlorofluorocarbons (CFC’s )


III. Structure of the atmosphere

A. Pressure changes

1. Pressure is the weight of the air above

2. Average sea level pressure

a. Slightly more than 1000 millibars

b. About 14.7 pounds per square inch

3. Pressure decreases with altitude

a. One-half of the atmosphere is below 3.5 miles ( 5.6 km )

b. 90 % of the atmosphere is below 10 miles ( 16 km )


B. Atmospheric layers based on temperature

1. Troposphere

a. Bottom layer

b. Temperature decreases with altitude - called the environmental lapse rate

1. 6.5 0C per kilometer ( average )

2. 3.5 0 F per 1000 feet ( average )

c. Thickness varies - average height is about 12 km

d. Outer boundary is named the tropopause

2. Stratosphere

a. About 12 km to 50 km

b. Temperature increases at top

c. Outer boundary is named the stratopause

3. Mesophere

a. About 50 to 80 km

b. Temperature decreases

c. Outer boundary is named the mesopause

4. Thermosphere

a. Not well-defined upper limit

b. Fraction of atmosphere’s mass

c. Gases moving at high speeds


IV Earth-sun relations

A. Earth motions

1. Rotates on its axis

2. Revolves around the sun

B. Seasons

1. Results of

a. Changing sun angle

b. Changing length of daylight

2. Caused by Earth’s changing orientation to the sun

a. Axis is inclined 23 1/2 0

b. Axis is always pointed in the same direction

3. Special days (Northern Hemisphere)

a. Summer solstice

1. June 21 - 22

2. Sun’s vertical rays are located at the tropic of Cancer ( 23 1/2 degrees N latitude)

b. Winter solstice

1. December 21 - 22

2. Sun’s vertical rays are located at the Tropic of Capricorn ( 23 1/2 degrees S latitude)

c. Autumnal equinox

1. September 22 - 23

2. Sun’s vertical rays are located at the Equator ( 0 degrees latitude)

d. Spring equinox

1. March 21 - 22

2. Sun’s vertical rays are located at the Equator ( 0 degrees latitude )


V. Atmospheric heating

A. Heat is always transferred from warmer to cooler objects

B. Mechanisms of heat transfer

1.Conduction through molecular activity

2. Convection

a. Movement of a mass

b. Usually vertical motions

c. Horizontal motions are called advection.


3. Radiation ( electromagnetic radiation)

a. Velocity: 186,000 miles per second in a vacuum

b. Consists of different wavelengths

1. Gamma (very short waves)

2. X - rays

3. Ultraviolet ( UV )

4. Visible

5. Infrared

6. Microwaves

7. Radio ( longest waves )

c. Governed by basic laws


C. Incoming solar radiation

1. Atmosphere is largely transparent to incoming solar radiation

2. Atmospheric effects

a. Scattering

b. Reflection-albedo ( percent reflected )

c. Absorption

3. Most visible radiation reaches the surface

4. 50 % absorbed at Earth’s surface


D. Radiation from Earth’s surface

1. Earth reradiates radiation at the longer wavelengths

2. Longer terrestrial radiation is absorbed by

a. Carbon dioxide and

b. Water vapor

3. Lower atmosphere is heated from Earth’s surface


VI. Temperature measurements

A. Daily maximum and minimum

B. Other measurements

1. Daily mean temperature

2. Daily range

3. Monthly mean

4. Annual mean

5. Annual temperature range


C. Human perception of temperature

1. Anything that influences the rate of heat loss from the body also influences the sensation of temperature.

2. Important factors are

a. Air temperature

b. Relative Humidity

c. Wind

d. Solar radiation


VII. Controls of temperature

A. Cause temperature to vary

B. Receipt of solar radiation is the most important control

C. Other important controls

1. Differential heating of land and water

a. Land heats more rapidly than water

b. Land gets hotter than water

c. Land cools faster than water

d. Land gets cooler than water


Other important controls continued

2. Altitude

3. Geographic position

4. Cloud cover

5. Surface albedo


VII. World distribution of temperature

A. Temperature maps

1. Isotherm-a line connecting places of equal temperature

2. Temperatures adjusted to sea level

3. January and July used for analysis because they represent the temperature extremes

B. Global temperature patterns

1. Temperature decreases poleward from the tropics

2. Isotherms exhibit a latitudinal shift with the seasons

3. Warmest and coldest temperatures occur over land

4. In the Southern Hemisphere

a. Isotherms are straighter

b. Isotherms are more stable

5. Isotherms show ocean currents

6. Annual temperature range

a. Small near equator

b. Increases with an increase in latitude

c. Greatest over continental locations

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