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Atmosphere
Notes
The Atmosphere
The Earth's atmosphere is a thin
layer of gases that surrounds the
Earth.
It composed of 78% nitrogen
21% oxygen
0.9% argon
0.03% carbon dioxide
trace amounts of other gases..
Atmosphere
• The layer of gases
that surrounds the
Earth
• Consists of 4
layers;
troposphere,
stratosphere,
mesosphere, and
thermosphere
Layers of the
Atmosphere
Troposphere
• The troposphere is the lowest region in the
Earth's (or any planet's) atmosphere.
• On the Earth, it goes from ground (or water)
level up to about 11 miles (17 kilometers) high.
• The weather and clouds occur in the
troposphere.
• In the troposphere, the temperature
generally decreases as altitude increases.
Stratosphere
• The stratosphere is characterized by a
slight temperature increase with altitude
and the absence of clouds.
• The stratosphere extends between 11 and
31 miles (17 to 50 kilometers) above the
earth's surface.
• The earth's ozone layer is located in the
stratosphere.
• Ozone, a form of oxygen, is crucial to our
survival; this layer absorbs a lot of
ultraviolet solar energy.
• Only the highest clouds (cirrus,
cirrostratus, and cirrocumulus) are in the
lower stratosphere.
Bad Ozone = smog
in troposphere
Mesosphere
• The mesosphere is characterized by
temperatures that quickly decrease
as height increases.
• The mesosphere extends from
between 31 and 50 miles (50 to 80
kilometers) above the earth's
surface.
Thermosphere
• Thermosphere: The thermosphere is a
thermal classification of the atmosphere.
• In the thermosphere, temperature
increases with altitude. The
thermosphere includes the exosphere and
part of the ionosphere.
Exosphere
•The exosphere is the outermost layer of the Earth's
atmosphere. The exosphere goes from about 400 miles
(640 km) high to about 800 miles (1,280 km).
•The lower boundary of the exosphere is called the
critical level of escape.
•This is where atmospheric pressure is very low (the
gas atoms are very widely spaced) and the temperature
is very low.
Ionosphere
• The ionosphere starts at about 43-50 miles
(70-80 km) high and continues for hundreds
of miles (about 400 miles = 640 km).
• It contains many ions and free electrons
(plasma).
• The ions are created when sunlight hits
atoms and tears off some electrons.
• Auroras occur in the ionosphere.
What happens to
temperature as altitude
increases?
• In the Troposphere the
temperature decreases
What happens to air
pressure as altitude
increases?
• The air pressure decreases because
the air gets less dense (thinner)
How do heating differences of
earthly materials affect air
movement?
•Because earthly materials heat up
at different rates, some heat up
quicker causing the air above them
to warm up and rise. Cooler air
moves in to replace the warmer air.
Conduction
Conduction is the direct transfer of energy through direct
contact between atoms.
Thought Experiments: Conduction
Which is colder coming out of the freezer: a metal spoon
or a wooden spoon? Why? Which feels colder?
Is snow a good conductor or a good insulator?
Is the purpose of a good insulator to keep the cold out or
to keep the heat in?
Radiation
The method by which the sun's energy reaches the earth.
All objects radiate: hotter ones radiate more. Two
objects at the same temperature, and the same size do
not radiate the same amount of heat.
Thought Experiment: Being without a
coat in winter
If you stood without a coat on a winter day with no wind,
would you feel cold? (Hint: Think about radiation,
convection, conduction.)
What if the wind were blowing?
Discuss the concept of wind chill.
Convection
The motion or movement of large groups of
molecules based on their relative densities or
temperatures. (Warm air rises-less dense- and
cool air moves in to replace it.)
Thought Experiment: Convection on the Beach
You are camped on the beach. You are offered a bet to predict
the wind direction during the day and night. Would you bet?
What do you predict? (Hint: Convective currents move air away
from hot areas. Which heats up more, land or water? Which
cools first?
How does the atmosphere
affect the rate at which
heated surfaces cool?
• The
atmosphere
holds heat in
so the heated
surfaces cool
slower.
What are “greenhouse
gases?”
• Carbon Dioxide
• Water Vapor
• Methane
What is the Greenhouse
Effect?
• The greenhouse effect is an increase
in the temperature of a planet as
heat energy from sunlight is trapped
by the gaseous atmosphere. Excess
carbon dioxide and water vapor
increase this global warming effect.
How does the Greenhouse
Effect work?
• Solar Energy (sunlight) is short-wavelength
radiation which easily penetrates the
Earth's atmosphere and warms the Earth;
only about one quarter of incoming sunlight
is reflected by the atmosphere. The
warmed Earth emits long-wavelength
radiation (infrared waves or heat energy)
back into space; these longer waves are
mostly reflected back to Earth by the
atmosphere.
METHANE CONCENTRATIONS (PPM)
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1990
1970
1950
1900
1800
1700
1600
Methane
HUMAN POPULATION (BILLIONS)
1990
1990
1970
1970
1950
1950
1900
1900
1800
1800
1700
1700
Human
Methane
Population
1600
1600
6
1.8
1.6
5
1.4
4
1.2
1
3
0.8
2
0.6
0.4
1
0.2
00
Charting the Evolution of the
Earth’s Atmosphere
50
0
00
15
00
25
00
Carbon Dioxide
Nitrogen
Hydrogen
Oxygen
Other Gases
35
45
00
90
80
70
60
50
40
30
20
10
0
How did the evolution of living
things affect the evolution of
the atmosphere?
• As organisms started
photosynthesis, oxygen was
released into the atmosphere and
CO2 was used up.
DEW POINT
The Dew point is temperature at which
condensation or dew occurs.
It is reached when the air is cooled to
below its moisture capacity and becomes
saturated.
RELATIVE HUMIDITY
Relative humidity is the amount of water
vapor in the air compared with the amount
of vapor needed to make the air saturated
at the air's current temperature.
Why humidity can be less than 100% when it's
raining
Humidity is a measure of the amount of water vapor in
the air, not the total amount of vapor and liquid. For
clouds to form, and rain to start, the air does have to
reach 100% relative humidity, but only where the
clouds are forming or where the rain is coming from.
This normally happens when the air rises and cools.
Often, rain will be falling from clouds where the
humidity is 100% into air with a lower humidity. Some
water from the rain evaporates into the air it's falling
through, increasing the humidity, but usually not
enough to bring the humidity up to 100%.
The dewpoint temperature gives a much better
estimate of the amount of moisture actually
present in the air, which is very important in
determining precipitation amounts and even how
comfortable you feel
Let's compare very cold, 10-degrees
Fahrenheit air with a relative humidity of 100%
with 72-degree tropical air, also with 100%
relative humidity.
In both cases, the relative humidity is 100%,
but the cold air's dewpoint is 10 degrees and the
warm air's dewpoint is 72 degrees.
The higher the dewpoint temperature, the
more moisture in the air.