The Atmosphere
Composition, Structure and
Temperature
Weather
• The state of the
atmosphere at a
particular place for a
short period of time
• Changes hourly, daily,
and seasonally
Climate
• A generalization of
the weather
conditions over a long
period of time
Qualities Measured Regularly
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Air temperature
Humidity
Type and amount of cloudiness
Type and amount of precipitation
Air pressure
Speed and direction of the wind
Composition of the Atmosphere
• Major Components
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78% nitrogen
21 % oxygen
Almost 1% argon
Carbon dioxide and
other gases
Composition of the Atmosphere
• Variable Components
– Water Vapor
– Dust
– Ozone
• Pollution in the lower atmosphere
• Layer in the stratosphere that absorbs UV rays
Height and Structure of the
Atmosphere
• Pressure Changes
– Height—the closer to
Earth, the more
pressure
Height and Structure of the
Atmosphere
• Atmosphere divided according to
temperature
– Troposphere
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Layer in which we live
Turbulent weather
Temperature decreases with altitude
Outer boundary—tropopause—about 12
kilometers high
Height and Structure of the
Atmosphere
– Stratosphere
• Temperature stays relatively stable to a height of
about 20 km
• Temp begins a gradual increase until it reaches the
stratopause, about 50 km
• Ozone is concentrated in the stratosphere
Height and Structure of the
Atmosphere
– Mesosphere
• Temps decrease with height until the mesopause,
approximately 80 km above the Earth
• Temperature approaches –90°C
Height and Structure of the
Atmosphere
– Thermosphere
• No well-defined upper limit
• Temperatures of individual atoms and molecules
reach 1000°C, but the gases are so far apart, the
collective heat is insignificant
Height and Structure of the
Atmosphere
Earth-Sun Relationships
• Rotation
– Earth spinning on its
axis
– Circle of illumination—
the line separating the
dark half of Earth from
the lighted half
Earth-Sun Relationships
• Revolution
– Movement of the Earth around the sun
– Earth travels more than 107,000 km per hour
Earth-Sun Relationships
• Seasons
– The lower the angle of
the sun, the more
spread out and less
intense is the solar
radiation
– Also determines the
amount of atmosphere
the sun’s rays must
penetrate
Heat Transfer
• Conduction
– Heat transfer by touch—by molecular activity
• Convection
– Transfer of heat by liquids or gases moving
from one place to another
• Radiation
– Transfer of heat by electromagnetic waves
– Empty space
Solar Radiation
• Scattering
– Gases and dust in the atmosphere
– About 30% of the solar energy reaching the
outer atmosphere is scattered back into space
– Some solar energy is scattered in the
atmosphere
Solar Radiation
• Albedo
– Amount of radiation
that is reflected by the
Earth’s surface
Solar Radiation
• Absorption
– Nitrogen is a poor absorber
– Oxygen absorbs most of the shorter UV
radiation high in the atmosphere
– Ozone absorbs most of the remaining UV
rays in the stratosphere
– Water vapor absorbs most of the solar
radiation within the atmosphere
– No gases are effective at absorbing visible
light
Greenhouse Effect
• About 50% of solar energy that strikes the
top of the atmosphere reaches Earth’s
surface
• Earth is heated from the ground up
because of radiation hitting the surface
• Radiation hits the Earth; some bounces
back and hits particles in the atmosphere
which then bounces it back to the Earth