Transcript Geos 110 Winter 2011 Earth`s energy balance powerpoint

GEOS 110 Winter 2011
Earth’s Surface Energy Balance
1.
Energy Balance and Temperature
a. Atmospheric influences on insolation:
absorption, reflection, and scattering
b. What happens to incoming solar
radiation? (global scale; local scale
later)
c. Surface-atmosphere energy transfer
d. Greenhouse effect
e. Temp. distributions
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Radiation
Radiation is the transfer of electromagnetic (EM) energy via an electrical
wave and a magnetic wave. When this energy is absorbed by an object
there is an increase in molecular motion and hence in temperature.
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Sun: T~6000K
E~7.4 x107 W/m2 ,
lmax = 0.44 mm
Earth: T~300K
E~ 460 W/m2 ,
lmax = 9.66 mm
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Radiation Laws
1. All objects, at whatever temperature, emit radiant energy.
2. Hotter objects radiate more total energy per unit area than colder
objects.
E = s T4 (Stefan-Boltzman Law) s=5.67e-8 Wm2K-4
3. The hotter the body the shorter wavelength of maximum radiation
lmax = c / T(K)
(Wein’s Law) c=2897 mmK
4. Objects that are good absorbers of radiation are also good
emitters. A perfect absorber/emitter is called a blackbody.
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Insolation
What happens to incoming solar radiation (=insolation)?
It is absorbed, reflected, and scattered.
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b. What happens to Solar Insolation?
The global energy budget = a balance
between incoming solar radiation (+)
and outgoing terrestrial radiation (-)
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http://geography.uoregon.edu/envchange/clim_animations/gifs/three_rads_web.gif
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Absorption:

Reduces energy reaching Earth surface –
different gases absorb different wavelengths of
radiation
Scattering:

Radiation is redirected
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Scattering
• Gas molecules in the atmosphere scatter incoming solar
radiation in all directions, not just back into space
• The smaller molecules scatter shorter wavelength, blue light.
Gases and aerosols are more effective scattering different
wavelengths:
 Gas molecules are most effective scattering shorter
wavelengths of visual light (i.e. blue and violet),
 Aerosols scatter all wavelengths
Moonrise
Earthrise
b. What happens to Solar Insolation?
If we assume a constant supply of
incoming solar radiation:
On Average
50% does not reach surface:
 25% absorbed by atmosphere
(7% via ozone)
 19% reflected via clouds
 6% back scattered via
atmosphere
5%
5%
19%
19%
6%
6%
45%
45%
25%
25%
50% that reaches the surface:
 45% absorbed by Earth surface
 5% reflected by ground
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b. The Fate of Solar Insolation
5%
planetary albedo = 30%
(Average reflectivity)
19%
6%
45%
25%
Earth and Atmosphere
absorb 45% + 25% =
70% of solar
insolation
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Earth’s Energy Balance
1. Energy Balance and Temperature
a. Atmospheric influences on insolation:
absorption, reflection, and scattering
b. Fate of incoming solar radiation
c. Surface-atmosphere energy transfer
d. Greenhouse effect
e. Temp. distributions
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C.
Surface – Atmosphere Energy Transfer
Radiation Exchange:
 Earth emits radiation (longwave), almost like a
blackbody
 Most of this radiation
(96%) is absorbed by
the atmosphere
(Radiation emitted
by Earth)
Radiation absorbed
by atm.
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C.
Surface – Atmosphere Energy Transfer
Radiation Exchange:
Selective absorption
Atmospheric “window”
(Radiation emitted
by Earth)
Radiation absorbed
by atm.
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C.
Surface – Atmosphere Energy Transfer
Radiation Exchange:
Net loss of radiation
C.
Surface – Atmosphere Energy Transfer
Net Radiation = absorption of insolation
+ net longwave radiation
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C.
Surface – Atmosphere Energy Transfer
Atmosphere = net radiation deficit
Surface = net radiation surplus
Energy must transfer between the
surface and the atmosphere
 Conduction: transfers radiant energy into
Earth, and warms the laminar boundary
layer ( = thin layer of air above surface)
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Heat
Transfer
Mechanisms of Heat Transfer
C.
Surface – Atmosphere Energy Transfer
Convection moves
energy between
surface and
atmosphere:
Free convection:
Mixing related to differential
buoyancy
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http://nepalmountaintrek.com/images/paragliding.JPG
C.
Surface – Atmosphere Energy Transfer
 Convection moves energy between
surface and atmosphere:
Forced convection:
= disorganized flow
Hurricane Ike at landfall, Huston/Galveston, 13 Sep. 2008
http://en.wikipedia.org/wiki/Image:HGX_N0R_Legend_0.png
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C.
Surface – Atmosphere Energy Transfer
How does the surface energy surplus
get to the atmosphere?
1. Sensible heat:


Readily detected heat energy
Magnitude of change related to object’s
specific heat (J kg-1 K-1) and mass
2. Latent Heat:

Energy required to change the phase of
a substance
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C.
Surface – Atmosphere Energy Transfer
When radiation hits water (e.g., ocean, lake, moist
soil, plants that can transpire), energy that could
have gone to sensible heating is redirected to
evaporate some water.
Evaporation of water makes energy available to the
atmosphere that otherwise would warm the surface,
thus acting as an energy transfer mechanism.
There is no net energy loss
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C.
Surface – Atmosphere Energy Transfer
Surface surplus offset by transfer of
sensible heat(8 units) and latent heat
(21 units) heat to atmosphere.
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C.
Surface – Atmosphere Energy Transfer
Latent heat
(21 units) is a
bigger factor
than sensible
heat (8 units):
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C.
Surface – Atmosphere Energy Transfer
Latitudinal variations:
 Between 38°N and S = net energy surpluses
 Poleward of 38o = net energy deficits
 Winter hemispheres - Net energy deficits
poleward of 15o
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Earth’s Heat Budget
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Aerosols
- Aerosol = liquid or solid particle suspended in the atmosphere.
- Large quantity = concentration of 1000 / cm3.
(1 breath = 1000cm3 = 1 million aerosols)
- Tiny = micrometers = 1 millionth of a meter.
Aerosols are formed by human and natural causes (e.g., sea salt from ocean
waves; fine soil; smoke and soot from fires, vehicles, and aircraft; volcanic
eruptions).
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Sulfate particles produced from volcanic
eruptions causes a cooling of the surface.
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Earth's surface is 5 million kilometers further from the sun in Northern
summer than in winter, indicating that seasonal warmth is controlled by
more than solar proximity.
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Seasons & Solar Intensity
Solar intensity, defined as the energy per area, governs earth's seasonal
changes.
A sunlight beam that strikes at an angle is spread across a greater surface area,
and is a less intense heat source than a beam impinging directly.
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Earth's annual energy
balance between solar
insolation and
terrestrial infrared
radiation is achieved
locally at only two
lines of latitude.
A global balance is
maintained by excess
heat from the
equatorial region
transferring toward the
poles.
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Local Solar Changes
Northern
hemisphere
sunrises are in
the southeast
during winter,
but in the
northeast in
summer.
Summer noon
time sun is also
higher above the
horizon than the
winter sun.
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C.
Surface – Atmosphere Energy Transfer
Latitudinal variations:
 Energy surplus at low latitudes is offset by advection (horizontal
heat movement) of heat poleward by global wind (75%) and
ocean (25%) currents
Global Sea Surface Temperatures: Climatology:
http://www.cpc.ncep.noaa.gov/products/GODAS/clim_movie.shtml
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C.
Surface – Atmosphere Energy Transfer
Ocean currents:
1. Climate change could cause a shift in the position of some
ocean currents, through a variety of mechanism. Can you
identify any land regions where climate could be vulnerable to
shifts in nearby currents?
2. Are there any localities whose climate could cool even if the
average global temperature were to warm?
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• Daily Temp (NYC)
• Gases in DRY AIR
• Atmospheric Pressure and Altitude
• Thermal Structure of the atmosphere
•
Determined by energy source, density of layers and composition of layers
• Daily path of the sun for
• a location at ? latitude
• Effect of Sun’s angle of incidence
• Annual variation in daily duration of available insolation
Relationship between
mean monthly temperature
and latitude
• Continental effect and Marine effect