Transcript Our Atmosphere

Jennifer Pogue
March 6, 2012
Origin
 The earliest atmosphere was believed to be Hydrogen
and Helium
 Why? They were the most abundant gases of the
universe.
 Methane and ammonia were also found in high
concentrations.
Where did it go?
 It escaped into space.
 Why?
 Earth’s gravity was too weak to hold the light gases in
place.
The Second Atmosphere
 Steam vents and volcanoes vented gases which
collected in the atmosphere
 **We are assuming the gases vented by volcanoes then is
the same as the gases now.
 Water vapor (80%), carbon dioxide (10%), nitrogen
(~5%)
How did the composition change?
 CO2 –Locked into sedimentary rocks, i.e. limestone
 H2O—condensed to form the ground water or clouds
 The concentration of CO2 and H2O decreased leaving
N2 to increase in concentration .
 Nitrogen is relatively inactive chemically.
 Oxygen increased as plants converted carbon dioxide
through photosynthesis.
Proof is in the rocks
 Precipitation of limestone in great
quantities.
 The oxidation of iron to form banded
deposits in early rocks.
 The distribution of various minerals in
most early sedimentary rocks.
Evidence of an Early Atmosphere
Limestone
(Stone Museum)
Banded-iron
(Stone Museum)
Today’s Composition
 We have lots more oxygen (~21%) and lots less carbon
dioxide.
 Both of these are good things
Composition Comparison
78%
Nitrogen
4-6%
21%
Oxygen
<1%
0.9%
Argon
0-1%
0.033%
Carbon Dioxide
10%
0-4%
Water Vapor
80%
0-0.000007%
Ozone
0%
<1%
Other Gases
3-4%
Heat & our atmosphere
 Three methods heat moves through our atmosphere
 Conduction
 Convection
 Radiation
Layers
 Troposphere
 Stratosphere
 Mesosphere
 Thermosphere
 Ionosphere
 Exosphere
Troposphere
0-12 miles
 Thickness varies depending on where you are on earth.
Thicker around the equator. Thinner at the poles.
 Temperature decreases as you go up in the
troposphere.
 Most weather occurs here.
 The layer we are in.
 Most airplanes fly here
Tropopause (about 12 miles up)
 The boundary between the troposphere and
stratosphere
 The altitude where the temperature stops dropping
 It’s about -60°F
 90% of the atmosphere is below the tropopause.
Stratosphere (12-31 miles up)
 Lower limit mixes with the troposphere to form the jet
stream
 Air gets warmer as you increase in altitude
 Prevents convection causes the top of the anvil shaped
storm clouds (cumulonimbus)
 This is called a temperature inversion
 Why the temperature inversion?
 The ozone layer
 Considered part of the middle atmosphere
The Ozone Layer
 High concentration at about 15 miles up
 Absorbs most of the sun’s ultraviolet rays
 The absorption causes the temperature increase
Stratopause (31 miles up)
 The boundary between the stratosphere and
mesosphere
 The temperature stops increasing
 About 5°F
 99.9% of the atmosphere is below stratopause
Mesosphere (31 to 56 miles up)
 Gases get thinner and thinner
 Temperature decreases as altitude increases
 Molecules are very far apart
 Slow down meteors
 Part of the middle atmosphere
Mesopause
 The boundary between mesosphere and thermosphere
 Temperature stops decreasing
 Low temp is -184°F
Thermosphere (up to 375 miles)
 Known as the upper atmosphere
 The “Hot” Layer
 Ultraviolet and x-ray radiation
absorbed by the molecules in
this layer
 Auroras occur in this layer
Ionosphere
 Not really a layer of its own
 A part of the thermosphere
 Responsible for bouncing sound waves around the
earth
Exosphere (up to 6200 miles up)
 This is the layer in which atoms and molecules escape
into space and satellites orbit the earth.
Jennifer Pogue
March 6, 2012
Water
 The water can be in solid, liquid or gas form.
 In a gaseous form in our atmosphere, we call it water
vapor.
 It gets there through evaporation of surface water.
 The water removes heat from the surface as it
evaporates.
 Evaporation is a cooling process.
Phases changes
Humidity
 Water vapor present in the atmosphere
 Specific humidity
 The number of grams of water vapor per kilogram of air
 Capacity is different for every temperature.
 Capacity basically doubles for every increase of 11°C
 Relative Humidity
 Compares the actual amount of water vapor in the air to
the maximum amount of water vapor the air can hold
 Given as a percentage
Relative Humidity
The Equation
actual
R.H. 
x100
saturation
How is it measured?
 A sling psychrometer
 Measure the difference in temperatures
 Drier air  the more cooling from evaporation  the
greater the difference  the lower the relative humidity

If there is no difference, the air is saturated and won’t accept
any more water vapor.
The Dew Point
 The temperature at which saturation occurs and
condensation begins.
 As warm, moist air cools off over night, the cooler air
can hold less water vapor. The vapor condenses to form
suspended droplets (i.e. fog) or if on a surface, dew.
 You get frost if the air temperature is below 0°C.
 The more water vapor in the air, the less the air has to
cool in order for condensation to occur  higher dew
point.
Condensation
 Happens under two conditions:
 Have to have a material for water to condense onto
 Air must cool to or below its dew point
 The particles onto which condensation occurs are
called condensation nuclei.
 Usually “dirt” in the atmosphere
 Must have these to have fog!
Cloud Formation
1.
2.
3.
4.
5.
6.
Humid air rises
Air begins to cool
Cool air can’t hold as much water
Air temp reaches dew point temp
Air is saturated 100% relative humidity
Water vapor condenses to water drops around a
nuclei like dust particles or smoke (forms clouds)
Cloud Types
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Stratus—layered, low clouds
Cumulus—puffy clouds, group upward, flat bases
Cirrus—high, feathery clouds; like curls of hair
Nimbus—rain clouds
 Prefixes used:
 Strato-layered
 Cumulo-puffy
 Alto—mid-height
 Cirro—high in height
 Nimbo—dark, rain
Low Level Clouds
 Below about 2000 meters
 Stratus
 Nimbostratus
 Stratocumulus
Stratus
Uniform gray, cover the sky
Stratocumulus
Low, lumpy, gray
Nimbostratus
Dark gray, ragged, may or may not be able to see the edges
Altocumulus
About as wide as your thumb when you hold it at arm’s length
Altostratus
Usually form ahead of continuous rain/snow clouds
Cirrus
High, long, thin, wispy
Made of ice
Cirrocumulus
Long rows of small rounded puffs
Width of little finger when held at arm’s length
Cirrostratus
Sheet-like thin clouds that cover the sky
Usually a precursor to rain/snow
Vertical Cloud Development
 Clouds grow up into the atmosphere instead of
outward across the sky
 Develop by warm air rising from the surface
Cumulus
Cotton balls with definite outline and flat base
About the size of your fist or
larger when held at arm’s length
Nimbocumulus
Thunderstorm clouds
Works Cited
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Department of Maritime Civilizations - University of Haifa. “Earth
Origins and Formation.” 10 Apr 2006.
<http://maritime.haifa.ac.il/departm/lessons/ocean/lect03.htm>.
Pflueger, Nathan. “The Origins of the Atmosphere.” 14 Oct 2003.
11 Apr 2006.
<http://eugevir.tripod.com/origins/atmosphere.html>.
Stimac, John. “The Atmosphere – origin and structure.” 11 Apr
2006.
<http://www.ux1.eiu.edu/~cfjps/1400/atmos_origin.html>.
Stone Museum. “Types of Rock.” 10 Apr 2006.
<http://www.geol.sci.hiroshimau.ac.jp/~geotect/stonemuseum/Classification-j.html>.
http://www.srh.noaa.gov/jetstream/atmos/layers.htm
http://www.windows2universe.org/earth/Atmosphere/clouds/clou
d_types.html