Download 2.5 Earth`s Atmosphere

2.5 Earth’s Atmosphere
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The atmosphere is a thin sea of
air that supports life on Earth.
Gases and water vapor cause the
air to have weight and exert
pressure.
At sea level, the weight of air is
14.7 psi (pounds per square
in.) and has a maximum
pressure of 1 atmosphere.
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The lift on the top airplane wing and the suction on a straw or
vacuum cleaner is caused by decreased air pressure.
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Atmospheric Regions
Mesosphere
UV & Visible
light
Stratosphere
30 miles
50 km
Ozone
layer
Troposphere
Up to 11 miles
Snow from higher clouds
5 miles
Rain from
low altitude
clouds
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There are 4 layers in the atmosphere:
1. Troposphere (0-10 miles up) is where weather occurs.
- temperature decreases with altitude
- clouds, wind, weather fronts
Air in the troposphere is:
78% nitrogen
21% oxygen
0.93% trace gases – most of
which is Argon and other noble
gases, with some CO2, methane,
nitrous oxide, water vapor, and
ozone.
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There is more water vapor at the equator; less at the poles. This
is because colder air holds less moisture than warm air.
Equal amounts of cold air are
also heavier than warm air.
The increased weight creates pressure
differences that cause winds to develop.
Weather changes as cool,
heavy air moves toward
warm, light air.
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With a fixed amount of gas, when the pressure
is increased, the volume is decreased.
Gases and water vapor cause the air to have
weight and exert pressure.
The atmosphere is like a sea of air surrounding earth. At the top of
the atmosphere, there is less air and less pressure.
Atmospheric pressure and the air’s
density always decreases with height.
A barometer measures small changes in
air pressure. There are 2 types - aneroid
and mercury.
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If the barometric reading
indicates rising pressure, fair
weather is expected.
A decrease in the
barometric reading
indicates storm fronts.
If the barometer is steady, the weather won’t change.
At sea level, one atmosphere (1atm.) is the pressure required
to support 760 mm of Hg on a mercury barometer at 25 oC.
(The SI unit of pressure is the Pascal.)
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On top of Mt. Everest
(at 9000 meters
altitude) the air exerts
only enough pressure
to push a column of Hg
to 253 mm high.
Humidity refers to the amount of moisture or water vapor in the air.
As the temperature of the air increases, its capacity to hold more
water vapor increases.
When the air is filled to capacity with water vapor, it is saturated.
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2. Stratosphere (11 - 30 miles up) has similar gases to troposphere.
The ozone layer here protects Earth from the sun’s deadly UV
radiation. It traps heat and warms this layer.
NOAA
NOAA
- calm, no winds
- temperature
increases with
altitude
Launch of an ozonesonde
attached to a high-altitude
balloon from South Pole.
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3. Mesosphere (30-50 miles up)
Temperature decreases with altitude.
Sunclimate.NASA
4. Thermosphere (50-75 miles up)
Temperature increase with altitude.
These temperature reversals separate
the layers of the atmosphere.
The Thermosphere
Ionosphere Mesosphere
NOAA
Energetics and Dynamics
(TIMED) mission is studying
the influences of the Sun and
humans on these regions.
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