Solar & Terrestrial
Radiation
The Electromagnetic Spectrum
• Energy travel as waves and particles
• Energy is the capacity to do work
• E=MC2
– Where E is energy, M is mass and C is the
speed of light (300,000km/sec)
• Energy has electrical AND magnetic
properties
• ALL object ABSORB and EMIT EM
radiation
EM Radiation
• Described in terms of Wavelength or Frequency
• Wavelength distance between successive
crests or troughs in km, m, mm, mm
• Frequency # wave crest/time (1sec) cycles/sec
or Hertz (Hz)
• The longer the Wavelength (l) the lower the
frequency
• Frequency is inversely proportional to l, so the
higher the frequency the shorter the l
There is a simple relationship between the wavelength (l), frequency (n),
and velocity (c). If you know any 2 of them then you can compute the 3rd
using
c=ln
or, velocity (c) equals wavelength (l) times frequency (n).
EM Radiation
•
•
•
•
Travel through space
In a vacuum travel at the speed of light
Pass through liquids, solids, gases
EM radiation can be reflected, refracted when
crossing different mediums as well as absorbed
• Solar radiation arrives on Earth primarily as
visible (0.4-0.7 mm) and Ultra-violet and is
reflected and absorb and re-radiated to space as
visible and Infra-red (heat)
Radiation Laws
• Perfect radiator- blackbody
• Blackbody- at a constant temperature absorbs
ALL radiation that is incident on it and EMITS all
radiant energy it absorbs
• All known objects emit and absorb all forms of
EM radiation
• The l of most intense radiation (lmax) emitted by
a blackbody is inversely proportional to absolute
T of the object
 lmax=C/T where C is 2897 if l is in mm and T is in K,
where absolute zero is -273.15oC
– This is a statement of Wien’s Displacement Law
Wien’s Displacement Law
• Hot objects (stars) emit radiation that
peaks at relatively short wavelength
– The blackbody temperature is 6000K
– For the Sun it is about 0.5mm
• Cold objects (planets, like the Earthatmosphere system) emit peak radiation at
longer wavelengths
– The blackbody temperature is 288K (15oC)
– For the Earth it is about 10mm
Stefen-Boltzmann Law
• The total energy flux emitted by a blackbody
across all wavelengths (E) is proportional to the
fourth power of the absolute temperature (T4) of
the object
– E~T4
– A small change in temperature results in a greater
change in radiational energy emitted
– Since the sun radiates at a greater temperature than
the Earth the law predicts that the energy output per
square meter of the sun will be 190,000 times greater
than the earth
Input of Solar Radiation
• Stellar nuclear synthesis
– 80%hydrogen
– Hydrogen fusion  alpha particle Helium
– Internal temperature 20 million oC
• Photosphere- Visible solar surface 6,000oC
• Sunspots- cool areas of the sun’s surface
• Chromosphere- outward area, ions of H+ He+
4,000-40,000 oC
• Solar corona- highest level of solar atmosphere,
ionized gases, extending millions of kilometers
into space, where solar wind originates
Solar Altitude
• Intensity of solar radiation varies with
latitude
• Intensity of solar radiation varies with time
of day
• Intensity of solar radiation varies with path
through atmosphere gases
TEMPERATE
TROPIC
POLAR
Earth’s Motions in Space and the
Seasons
• Rotation on its axis every 24hrs (day)
• Revolution around the sun every 365.2422 days
elliptical orbit (year)
• Closest 3 January (perihelion) farthest 4 July
(aphelion), Earth receives 6.7% more radiation
at perihelion than aphelion
• Earth’s tilt at 23.5o
• Summer & Winter Solstice
– Tropic of Cancer & Tropic of Capricorn
• Equinoxes (March & September)
Solar Radiation & The Atmosphere
• Solar radiation interacts with gases and aerosols
• Scattering & reflection (albedo), absorption
(absorptivity) or transmissivity (amount that
reaches earth’s surface) of solar radiation must
equal 100%
• In scattering a particle disperses solar radiation
in all directions
• Scattering by molecules is wavelength
dependent and preferential scattering of blueviolet light by N2 and O2 is the reason for the
daytime sky
• Water and ice scatter visible light equally at all
wavelengths so that clouds appear white
Albedo
• Fraction of total radiation reflected by an
object (surface).
• Varies according to:




Cloud cover.
Particles in air.
Angle of sun’s rays.
Types of surface.
Stratospheric Ozone
• Ozone is a gas made up of three oxygen atoms (O3).
• Ozone is destroyed when it reacts with molecules containing
nitrogen, hydrogen, chlorine, or bromine. (CFCs)
• Ozone protects life on Earth from the Sun’s ultraviolet (UV)
radiation.
• Ozone screens all of the most energetic, UV-c, radiation, and
most of the UV-b radiation.
• Ozone only screens about half of the UV-a radiation.
Excessive UV-b and UV-a radiation can cause sunburn and
can lead to skin cancer and eye damage.
• In the lower atmosphere (the troposphere) near the Earth’s
surface, ozone is created by chemical reactions between air
pollutants from vehicle exhaust, gasoline vapors, and other
emissions.
• At ground level, high concentrations of ozone are toxic to
people and plants.
The Ozone Layer
• The depletion of the ozone (O3) layer was first
reported in 1985 by British scientists who said
the amount of ozone had been decreasing over
Antarctica since the late 1970s
• Depletion of the ozone layer over the poles is
most severe in the winter months
• The greatest loss is over Antarctica because
Antarctic winters are colder than Arctic winters
• The ozone hole grew to its largest recorded size
in 2000, expanding to an area roughly three
times the size of the United States
• Satellites carrying total ozone mapping
spectrometers (TOMS) have been used to map
the zone since 1978
Map of ozone over Antarctica (1997) in Dobson
units [0.01mm thickness of ozone at standard P
& T (0oC and 1 atm)]
Ozone Problem
• Decreased levels of ozone in the atmosphere will
allow more ultraviolet radiation to reach the surface
• A 50% decrease in ozone is estimated to cause a
350% increase in ultraviolet radiation reaching the
surface
• Ultraviolet radiation is known to adversely affect
growth and reproduction in organisms and is thought
to increase the risk of skin cancer and cataracts
• Research also indicates that increased ultraviolet light
may decrease rates of photosynthesis and growth in
marine plants, phytoplankton, by about 2–4% under
the Antarctic ozone hole
OZONE
• Thanks to the UN Montreal Protocol
• The production and consumption of entire
groups of harmful ozone-depleting
chemicals has been successfully phased
out in developed countries, and the same
process is now well under way in
developing countries.
• Overall, almost ninety five per cent of all
ozone-depleting substances have been
phased out
After 20 years of
protecting the ozone layer
with a new generation of
chemicals, governments
are now having to confront
the fact that these ozonefriendly substitutes for
chlorofluorocarbons
(CFCs) also happen to be
greenhouse gases that
contribute to global
warming.
Intensity of solar radiation
• The Earth receives solar radiation
unequally over its surface
• The intensity per unit area of surface is
greatest at the equator
• Intermediate in the middle latitudes
• The lowest intensity is at the polar regions
Global Solar Radiation Budget
•
•
•
•
Reflected 31%
Absorbed by atmosphere 20%
Absorbed by Earth’s surface 49%
Earth’s climate is controlled by a Greenhouse
Effect
• Gases in the atmosphere control this effect
– H2Ovapor, CO2, O3, CH4, N2O
– The percent of IR radiation absorbed varies with l
– An Atmospheric Window is a range of l over which
little or no radiation is absorbed
– A visible window extends 0.3-0.9mm and major IR 813 mm, the peak IR emission of the planet is at 10mm
Absorptivity is very low or near zero in atmospheric window
Greenhouse Gases
• CO2 is stored in four reservoirs: three that are
active and one inactive reservoir including
–
–
–
–
the atmosphere,
the oceans,
the terrestrial system
Earth’s crust
• Most CO2 is stored in the oceans while the
smallest amount is found in the atmosphere.
• Short-wavelength incoming radiation is not
blocked by CO2, but re-radiated longwavelength energy is, and this warms the
atmosphere causing the greenhouse effect
Greenhouse Gases
• Changing atmospheric chemistry can be
monitored for past years by analyzing bubbles
trapped in polar ice.
• It can be demonstrated that following the
Industrial Revolution, the concentration of CO2
has risen dramatically and continues to rise at
an increasing rate.
• The concentration of CO2 in the atmosphere has
increased from 280 ppm to 380 ppm since 1850
• Currently, the average increase in concentration
is about 1.4 ppm per year
Past Climate in Ice
• Polar ice sheets (Greenland and Antarctica)
• Ice cores preserve a detail make up of the
ocean and atmosphere
• Trapped bubbles contain gases from the past
• GRIP (Greenland Ice Core Project) drilled a
core 3029m a record of more than 200,000
yrs
• Identify volcanic events, lead production,
large scale pollution
• Pre and post industrial revolution levels of
sulfate (3X) and nitrate (2X)
• Russian core at Vostok (3623m ~ 450,000
yrs)
– CO2 increased 140K and decreased 100K; 10K
increase by 40%
Ice Core
Ice
Core
CO2
• Scientists have estimated that the
greenhouse effect may produce a
global warming of 2–4°C over the next
hundred years.
– This could melt high latitude ice and raise
sea level by as much as 1 m by the year
2100.
• Careful measurements of short term
increases in global temperatures have
shown a twenty year warming period
which began in 1920 and another
period of warming that began in 1977
and continued through the 1980s
CO2
• There is considerable debate over the
actual cause or causes of the
observed global warming and
different mechanisms have been
proposed to explain it including:
– increasing levels of CO2,
– variations in sun spot cycles, and
– changing concentrations of dust particles in
the air
CO2
• Some natural processes actually lead to global
cooling. Massive volcanic eruptions can release
enough ash to the air to block incoming solar
radiation and cool the planet for a period of time
• The use of fossil fuels and the burning of tropical
forests produces about 7 billion tons of CO2
annually.
• Roughly 3 billion tons are stored in the
atmosphere, another 2 billion tons enters the
oceans and ocean sediments
• At least 1 billion tons are taken up by plants in
the re-growth of logged forests
FUTURE
• Sharp reduction in coal & oil consumption
• Greater reliance Non fossil fuel energy
resources
• Higher energy efficiencies
• Halt deforestation
Monitoring Radiation
• Pyranometer measures solar radiation
striking horizontal surface
• Transmits total (direct plus diffuse) short
wave (< 3.0mm) radiation
• Black and white surfaces (differences in
absorptivity and albedo) mean a different
temperature response (W/m2)
• Infrared Radiometer measures IR emitted
by objects
Solar Power
• Solar power is a clean, reliable form of
renewable energy generated by converting
energy from the sun's radiation into electricity
• Solar cells, also referred to as photovoltaic (PV)
cells are grouped and connected together in a
single frame called a panel or module
• These cells are comprised of special semiconductive materials, which is most often a
piece of silicon positioned under a layer of thin
glass
The world's largest solar electric power plant
The Gut Erlasee Solar Park, a 12-megawatt facility
Located near the Bavarian town of Arnstein, Germany
Solar Power
• Concentrating Solar Power (CSP): systems are
based on a series of mirrors or reflectors that
focus the sunlight into a central photo receptor
• These systems tend to be very large and
produce hundreds of megawatts of power.
• Australia will invest $320 million to construct the
world’s largest solar power plant
• The plant, which will be built in Victoria state, will
have a capacity of 154 megawatts and will be
built over the next several years, with a
completion date set for 2013
Australia