Transcript The Atmosphere

The Atmosphere
Composition, Structure, & Heat
Budget
Atmospheric Composition
• Reported on a dry basis, water vapor
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•
excluded since it’s so variable.
Only 2 gases comprise 99%
Water vapor normally <1 - 4%
Minor gases exert
influence far greater
than their abundance
would suggest, e.g.
greenhouse effect, UV
protection,
photosynthesis, etc.
Atmospheric Pressure
• A measure of the mass
per unit area of air.
• Increases as the density of
air increases because a
volume of air with high
density has more gas
molecules than a volume
with a lower density.
• Decreases with altitude.
Dynamic
Equilibrium of
Atmospheric
Water Vapor
• Atmospheric water vapor
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•
•
varies immensely with place
and time.
For Earth as a whole,
evaporation equals
precipitation.
For ocean as a whole,
evaporation exceeds
precipitation.
Latent heat of vaporization
supplies much of the heat to
drive convection.
Air Parcel Size and Temperature
• Rising and
cooling
triggers
condensation
which forms
clouds and
rain.
• Latent heat
released at
condensation
further warms
air and forces
more rising.
Layers of the Atmosphere
•
The inner most layer is the troposphere. It is mostly nitrogen and
oxygen. Chemical cycling occurs in this layer. Responsible for
the planet’s weather and climate.
•
The second layer is the stratosphere. Contains less matter than
the troposphere. Ozone concentration is high, water
concentration is very low.
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The third layer is the mesosphere. This gives way to the
thermosphere.
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The exosphere is the last layer and it tails off into space and
meets the solar wind.
•
The ionosphere straddles several layers. The ionosphere
reflects radio waves & hosts the aurora borealis & aurora
australis.
TROPOSPHERE
Structure & Temperature Profile of Lower Atmosphere
• Virtually all weather occurs in troposphere.
• Earth’s surface heats troposphere from bottom; favors vertical mixing.
• Stratosphere heated most at middle & top because of UV ray absorption by
ozone; limits vertical convective mixing there.
strongest
heating by UVabsorbing
ozone
heating from below
Sun Angle Controls Sunlight
Intensity
• At low angles, sunlight spreads over much
•
larger areas & thus heats less effectively.
At low angles, sunlight reflects from water &
ice more efficiently.
Variation of Solar Radiation with Latitude (also
with Seasons and with Time of Day)
At winter solstice
(N.H.) the most
intense radiation is
at Tropic of
Capricorn @ noon.
noon radiation
intensity (cal/cm2/min.)
at given latitude
on equinox days:
@40o = 1.53
@66.5o = 0.80
@89.5o = 0.02
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These numbers indicate global averages. Global Heat Budget
Locally the energy fluxes vary with season, time of day, cloud cover,
snow cover, vegetation patterns, etc.
Greenhouse
Effect
=
+
X 5%
X 16%
Absorbed Visible Light Converted to
IR, Sensible & Latent Heat
X 39%
Latitudinal
Variations in
Radiation Budget
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Garrison,
2005
Excess heat lost near poles must be carried from
tropics to poles by ocean currents & winds.
Surplus
must
equal
deficits to
maintain
heat
budget.
Poleward Heat
Transport to
Balance
Unequal
Heating
• Equator
•
would be
hotter & poles
would be much
colder without this
transport.
Transport by winds
& ocean currents.
Garrison,
2005