Download The Atmosphere: Earth-Sun Relations, Energy Balance, Global

The Atmosphere:
Earth-Sun Relations, Energy Balance, Global Warming
What are the major physical processes responsible for the daily, seasonal, and spatial differences
in weather and climate on earth? What causes inter-annual and longer term climate change?
What is predictable about Earth’s climate? How is human activity causing climate change?
Earth-sun distance & angle, radiation transfer, structure and composition of earth’s atmosphere.
What is predictable about Earth’s climate?
1.  Diurnal cycle
2.  Seasonal cycle
3.  El Nino/Southern Oscillation (ENSO)
4.  Anthropogenic global warming
5.  Milankovitch orbital cycle
Net Radiation Flux
Seasonality of the radiation budget at the surface of Earth
Net radiation flux = balance between incoming and outgoing
energy at the top of the atmosphere.
Note the variations in intensity within a latitudinal band.
What causes this seasonal cycle in the distribution of surface radiation
budget?
June 2006
July 2006
Sept 2006
Dec 2006
What causes the seasonal cycle?
Earth’s elliptical orbit (perihelion vs. aphelion)?
Mean Earth – Sun distance = 150 million km (93 million miles).
Between perihelion and aphelion there is a
3% difference in distance, but a 7% difference in total radiation load to Earth.
Perihelion occurs during the Northern Hemisphere winter!?
What causes the seasonal cycle?
Answer? = Earth’s axial tilt
66.5º off of the plane of the ecliptic
(23.5º off perpendicular)
very important numbers!
(also orbit, parallelism, & sphericity)
(tilt caused by Mars-size bollide
that struck earth and formed moon??)
Axial tilt, parallelism, and the seasonal climates of Earth
Circle of illumination, subsolar point, declination, solstice, equinox, tropics, Arctic & Antarctic Circles
North
North
Dec 21
March 20
June 21
Sept 20
Declination of the Sun
Solar Angle (for 40ºN/S)
Declination of the Sun =
Solar Angle (‘elevation angle of the sun’) =
latitude of subsolar point at noon,
365 declinations per year,
from 23.5ºN to 23.5ºS
Solar angle is a direct measure of solar radiation
intensity (shadow length at noon, is an inverse measure of
solar radiation intensity)
Fayetteville = 30.5 to 77.5º (Dec. to June solstices)
Milankovitch Orbital Parameters
Eccentricity
100,000 year period
Obliquity
41,000 year period
Precession
23,000 year period
Milankovitch orbital variations and ice age climate change (variations = gravity, especially from Jupiter & Saturn)
Eccentricity of orbit (100kyr), obliquity of axial tilt (41kyr), precession of equinox + perihelion (23kyr)
Variations in the Earth's Orbit: Pacemaker of the Ice Ages
J.D. Hays, J. Imbrie, N.J. Shackleton
Science 10 December 1976
One of the most famous examples of Milankovitch
Forced cycles, the Triassic dolomite platform which
makes up the famous dolomite mountains in Italy
(photos by Jack Brauer)
One of the great scientific discoveries of the ODP, and one of the greatest contributions of
Paleoclimatology. Ocean sediment cores cover the last 5.5 million years and record onset of
Antarctic glaciation. Note shift in the dominance of the 41kyr obliquity and 100kyr eccentricity
quasi-cycles. Benthic isotopes scaled to surface air temperature at Vostok on Antarctic Plateau.
The Electromagnetic Spectrum of radiant energy: “The Mighty Kingdom”
Longwave (LW)
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8.
Visible
(H. Hertz)
Shortwave (SW)
Everything >0.0K emits ‘EMR’ (temperature = random atomic/molecular motion, range = >0 - 1023K).
Discriminate EMR by wavelength (or inversely by frequency).
Huge range of wavelengths (or frequencies), vary by a factor 1022
Three categories: Longwave, Visible, Shortwave (LW = terrestrial, infrared, radio; SW = solar, ultraviolet).
SW EMR dangerous (ultraviolet = skin cancer; gamma radiation deadly, e.g., Chernobyl, Fukushima)
Visible EMR only a tiny fraction of the spectrum, 0.4 to 0.7 microns, principal wavelength of solar radiation at
earth’s surface (optical evolution of humans & kestrels), rainbow colors (Newton);
color of objects = absorbed vs. reflected EMR (leaves absorb red and blue, reflect green).
Human eyes detect visible EMR, but we ‘sense’ infrared and ultraviolet (thermal sensing and sunburn).
Most solar radiation to earth surface is visible EMR, most terrestrial EMR to space is infrared (or LW EMR).
Black Body Emission Spectra of the Sun and Earth
The hot sun emits huge
amounts or shortwave
radiation.
Sun = .4 - .7microns (µ)
Earth = 10.0 – 20.0 µ
The cool earth emits less
radiation at longer
wavelengths.
Black Body Emission Spectra of the Sun and Earth
The hot sun emits huge
amounts or shortwave
radiation.
The cool earth emits less
radiation at longer
wavelengths.
Solar and Earth blackbody radiation
emission spectra plotted on the
same scale
Stefan-Boltzman Law:
R = σT4
The amount of radiation emitted by an
object (R) is proportional to the 4th power of its
temperature (T), measured in Kelvin units.
σ = the Stefan-Boltzman constant
(5.735 x 10-5 Langleys/minute/degree K4)
Wein’s Displacement Law:
λmax = 2897/T x 10-6 meters
The wavelength (or type) of maximum
radiation emission (λmax ) of an object is an
inverse function of its temperature (T).
Applications? Can calculate the temperature and total
radiation output of the sun (& stars, planets). Begin with
a radiometer.
Bottom line, sun is hot (6000K, 5700ºC) and emits huge
amounts of shortwave radiation. Earth is cool (290K, 15 ºC)
and emits much less longwave radiation.
Albedo side
The Energy Balance of Earth
Greenhouse side
Global Energy Balance = Incoming solar (SW) vs. outgoing terrestrial radiation (LW), it must balance.
Follow 100 units of incoming solar radiation, Ozone in stratosphere absorbs 3%, then shed as LW to space;
-31% = albedo = reflectivity or ‘Earthshine’ (= dust, clouds, color & texture, albedo feedback example on balance).
Direct warming of lower atmosphere by solar radiation is limited, +21%.
Solid earth & oceans absorbs 45% of incoming solar & acquire heat (direct & diffuse beam solar). Blue sky?
Earth & lower atmosphere are heated by absorbing 66% of incoming solar radiation (21 + 45%).
Latent & sensible transfers also move heat into atmosphere. Earth then re-radiates longwave EMR (infrared).
Note balance & recycling of infrared radiation by atmospheric system (‘counter-radiation’ = greenhouse effect,
atmospheric absorption by water vapor, clouds, carbon dioxide…alter those and you alter the energy balance).
-69% incoming solar radiation shed to space as terrestrial radiation, the global energy budget is balanced!
[Venus(900°F), Mars (-67°F), both super greenhouse conditions with >95% CO2].
Earthshine on the Crescent Moon
Sunlight illuminates the crescent, ‘earthshine’ illuminates the remainder of the moon surface (earth’s albedo). NASA
The solar radiation spectrum
The protective atmosphere, ozone (O3) absorbs
biologically harmful ultraviolet radiation (UV-B, in
the 0.2 to 0.4 micron range)
The earth radiation spectrum
The greenhouse effect of the atmosphere, CO2 and H2O
absorb some of the longwave radiation (or infrared thermal
emissions) that would otherwise escape to space to warm
the atmosphere and surface of Earth (especially in the 13
to 17 micron range).
The detailed EMR absorption spectra of CO2 and H20:
NASA
Without an atmosphere, life on Earth would not exist as we know it