Atmosphere Notes
I. Atmosphere
A. Envelop of gases that surround our earth
B. Gases are kept on our planet by the force
gravity.
C.First Atmosphere
1. Mostly H2 and He
2. Earth was not fully developed yet
D.Second Atmosphere
1. Now volcanoes began erupting
2. Out gas different material
3. Different gases were put into the
atmosphere
a. H2O, CO2, SO2, CO, S2, Cl2, N2, H2) and
NH3 (ammonia) and CH4 (methane)
b. No oxygen
E. The beginning of the modern atmosphere
1. Life appeared about 2.0 to 2.8 billion years
ago
2. The beginning of photosynthesis and the
addition of oxygen into the atmosphere
3. Evidence
a. Banded iron formations
b. Red Beds
F. Troposphere
1. 0-18 km
2. Weather occurs
3. Temperature goes down (6.5oC per km)
4. Ground stores the heat
G. Tropopause: Pause in temperature change
H. Stratosphere
1. 18 to 50 km
2. Contains ozone (three oxygen atoms)
3. Heats up as you go up because of the ozone
I. Stratopause: Pause in temperature between
Stratosphere and Mesophere
J. Mesophere
1. Temperature decreases
2. 50-85 km
K. Mesopause: Pause in temperature between the
mesosphere and thermosphere
L. Thermosphere
1. 85 km to 400 km
2. Temperature increases
3. Contains the ionosphere
M.
Exosphere
1. 400 km to 10, 000 km
2. Boundary between atmosphere and space
II. Atmospheric Pressure
A.Atmospheric pressure is defined as the force
per unit area exerted against a surface by the
weight of the air above that surface.
B. Pressure=Force/Area
C.Measured with a barometer
D.For every 5.6 km you ascend, there is half the
atmosphere mass above you when you started.
III. Tropospheric Lapse Rate
A.The decrease in temperature as you go higher
in the troposphere.
B. Dry rate is 5.5 oF per 1000 feet
C.Wet rate is 3.5 oF per 1000 feet
D. Areas that receive more heat have thicker
troposphere layers.
IV. Changes in pressure
A.What causes differences in pressure?
a. The unequal heating of the planet
1. Earth’s Energy Budget
i. Albedo: The fraction of solar
radiation that reflects off an object
2. Latitude
i. Change as you north
ii. Sun’s angle hitting earth
iii. Energy differences
3. Elevation
i. Higher elevation colder
temperatures
ii. Decrease in temperature as you
move through the troposphere
4. Tilt of Earth
i. 23.5 degrees
ii. Gives seasons
iii. Differences in heating the earth
5. Global Air Circulations
i. Global wind patterns
ii. Transfer heat and moisture
iii. Winds flow from High to low
pressure
6. Global Ocean Currents
i. Moves warm water toward the
poles
7. Proximity to bodies of water
i. Moisture content will higher
next to a body of water
ii. Lake Effect snow
b. Mountains and Rain Shadowing
i. Mountains stop moisture from going over
mountain
ii. Leeward side there is a desert
iii. North side versus south side
1. South side is always warmer
V. High and Low Pressure
a. High pressure: Area that has pressure higher then
surrounding air.
i. Associated with divergence on the
surface and convergence in the upper
atmosphere.
b. Low Pressure: Area that has pressure lower then
surrounding area.
i.
Associated with convergence on
surface and divergence in the upper
atmosphere.
c. Measuring Atmospheric Pressure
i. Barometer
ii. Isobar
iii. Normal Pressure is roughly
760 mm, 29.9 inches of
mercury, or 1013 mb
VI. Air movements
a. Pressure Gradient Force: The force of the
movement of the winds.
i. Air moves from a high to low
ii. The closer the isobars the steeper the gradient
force.
iii. The closer the isobars the stronger the
winds.
b. Coriolis Effect
i. A force that appears to deflect winds to
the earth’s rotation
1. Northern Hemisphere
deflects to the right
2. Southern Hemisphere
deflect to the left
c. Friction Force
i. A force that drags on the wind as it
crosses the surface.
a. Wind decreases with more contact to
the surface.
d. Air movement around a high and low
i. High
a. Rotates out of the high in a clockwise
fashion: Anticyclonic Flow
ii. Low
a. Rotates out of the high in a
counterclockwise fashion: Cyclonic
Flow
iii. It is reversed in the southern hemisphere
VII. AIR MASSES
a. An air mass is a large body of air
i. Sub continental in size
ii. Several miles high
b. With uniform temperature and moisture conditions
c. SOURCE REGIONS - WHERE AIR MASSES
ACQUIRE THEIR PROPERTIES
d. NORTH AMERICAN AIR MASS SOURCE
REGIONS
Air Masses are Classified According to:
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
Surface of source region
 Continental (c) Forms over land - dry
 Maritime (m) Forms over ocean - moist
Temperatures
 Tropical (T) -Low latitudes - warm
 Polar (P) - High latitudes - cold
 Arctic (A) - Poles - very cold and dry
e. FRONTS
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Fronts are boundaries that separate air masses
There are four types of front:
 Stationary front
 Cold front
 Warm front
 Occluded front
STATIONARY FRONTS
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Cold and warm air masses next to each other
Neither air mass advances
COLD FRONT
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Cold air replaces warm
Much steeper than warm fronts
Advances faster than warm front
More violent weather -cumulonimbus clouds
Short, sharp showers
WARM FRONT

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Warm air replaces cold
Gentle slope (1:200)
Covers a wide area with its weather
Stratus clouds get lower as front approaches
Drizzle or steady rain
OCCLUDED FRONTS
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Cold front overtakes the warm front
Lifts the warm air off the ground
Clouds and rain possible
f.
g. Cyclone evolution and occluded fronts
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Mid-latitude cyclones evolve over several days
while progressing eastward
Initially open wave with cold and warm fronts
separated by warm sector
Cold front moves faster than warm front, begins
to catch up and push warm sector off the ground
Eventually warm sector lifted completely off the
ground, producing occluded front