Transcript solar radiation

ATMOSPHERE AND SURFACE ENERGY
BALANCES
•
ENERGY PATHWAYS AND PRINCIPLES
•
ENERGY BALANCE IN THE TROPOSPEHERE
•
ENERGY BALANCE AT EARTH’S SURFACE
•
SOLAR ENERGY – ENERGY OF THE FUTURE?
Kuala Lumpur, capital city of Malaysia with the Petronas Twin
ENERGY PATHWAYS AND PRINCIPLES
(I) Insolation
(II) Transmission
(III) Refraction
(IV) Albedo and Reflection
(V) Clouds and the Atmosphere’s Albedo
(VI) Scattering and Diffuse Radiation
(VII) Absorption
(VIII) Conduction, Convection and Advection
INSOLATION
• Solar radiation that reaches a horizontal plane at Earth is called
INSOLATION
• Insolation means “Intercepted Solar Radiation”
• Insolation refers to the input of Solar Radiation into the EarthAtmosphere system
• Insolation at the top of the atmosphere is expressed as the SOLAR
CONSTANT (1.94 cal/m2/min-1)
• Insolation is the single energy input driving the Earth-Atmosphere
system
• Insolation also includes all the radiation that arrives at the earth’s
surface, both DIRECT RADIATION and DIFFUSE RADIATION
• The distribution of insolation is UNEVEN through the different layers of
the atmosphere
• The distribution of insolation is UNEVEN on the Earth’s surface
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Insolation at the Earth’s surface is unevenly distributed.
Which are the “Source” areas and which are the “Sink”
areas?
What are the factors causing the uneven distribution of
insolation on the earth’s surface?
•
Solar Output – solar maximum (sunspots) & solar minimum
•
Curvature of the earth’s surface & Latitude
•
Earth’s tilt & Seasons
•
Clouds
•
Atmospheric pollutants
•
Surface characteristics:
(I)
land or sea
(II)
dark or light
(III)
rough or smooth
(IV)
urban or rural
(V)
type of land use
(VI)
Orientation or Slope Angle (Aspect)
(VII) Total Albedo
SOLAR OUTPUT – Solar Radiation is at a maximum during sunspots or
Solar maximums & at a minimum during Solar Minimums – 11 year-cycle
EARTH’S CURVATURE - Curvature of the earth’s surface & Latitude result
in Equatorial areas receiving more solar radiation than Polar areas
Solar radiation is
diffuse in Polar areas
Solar
radiation is
concentrated
in Equatorial
areas
Solar radiation is
diffuse in Polar
areas
EFFECT OF SLOPE ORIENTATION ON INSOLATION
North slope is always in the
shade – less solar radiation
South slope is always in the
Sun – More solar radiation
North slope is always in the
Sun – More solar radiation
South slope is always in the
shade – Less solar radiation
North Slope
South Slope
North Slope
South Slope
TRANSMISSION
•Transmission refers to the the passage of LONGWAVE
and SHORTWAVE energy through either the atmosphere or
water
• During the DAY, transmission of SHORTWAVE solar
radiation takes place in the form of radiation inputs – UV-A,
UV-B, UV-C, VISIBLE LIGHT and NEAR-INFRARED
wavelengths
• At NIGHT, transmission of LONGWAVE thermal Earth
radiation (thermal infrared) takes place as radiation
outputs, passing through the atmosphere into space
A simplified model of the Earth-Atmosphere energy system –
notice that incoming transmission of daytime solar radiation
is balanced by outputs of earth radiation transmission at
night.
REFRACTION
• When insolation enters the atmosphere, it passes from one medium
(empty space) to another (atmospheric gases), or from air into water.
When this happens, it subjects the insolation to a change of SPEED which
also shifts its DIRECTION
• This causes the insolation (light) to BEND – a bending action called
REFRACTION
• An example of refraction is light passing through a PRISM which refracts
light, bending different wavelengths to different angles, separating the
light into its component colors to display the spectrum
• Another example of refraction in nature is the RAINBOW which is formed
when visible light passes through myriad raindrops & is refracted and
reflected to us at a precise angle
• A MIRAGE (an image appearing near the horizon) is another example of
refraction where light waves are refracted by layers of air of different
temperatures on a hot day
• A final example would be the refraction of the image of a SETTING SUN
over the horizon. Light from a low sun must penetrate more air before
reaching us & is refracted by different layers of air (of different densities).
REFRACTION
The setting Sun here is only a MIRAGE!
The Sun has actually gone below the Horizon
We still see it because it is Refracted over the horizon for about 4 minutes
We also see the Sun earlier during sunrise, about 4 minutes earlier
Hence, REFRACTION has added 8 minutes of DAYLIGHT each day!
ALBEDO and REFLECTION
• Albedo is related & dependent on the rate of reflection of
insolation, the higher the reflectance the higher is the Albedo
• Why is there reflection? This is because a portion of
insolation passes through the atmosphere, reaches the earth
surface & bounces back into space without performing any
work, i.e. without being absorbed
• Albedo is the reflective quality (or brightness) of a surface,
the brighter a surface the more reflective it is
• Hence, Albedo is defined as the “Percentage of Reflected
Insolation”
• 0 % Albedo is TOTAL ABSORPTION
• 100 % Albedo is TOTAL REFLECTANCE
• See some examples of albedo values in the next slide
Albedo values
(% reflected)
6–8%
Fresh snow
80 – 95 %
Earth’s albedo
(average) = 31 %
Water bodies 10 – 60
% (low solar angles =
greater reflection)
Forests 10 – 20 %
Crops,
grasslands
10 – 25 %
Grass 25 – 30 %
Asphalt 5 –
10 %
Dark roof
8 – 18 %
Light roof
35 – 50 %
Brick, Stone
Dry concrete
20 – 40 %
17 – 27 %
TOTAL ALBEDOS FOR
JULY AND JANUARY
WHICH ARE THE HIGH
ALBEDO AREAS?
•NORTH & SOUTH POLES
July
0%
•DESERT AREAS
WHICH ARE THE LOW
ALBEDO AREAS?
•THES SEAS AROUND THE
January
TROPICS
•EQUATORIAL AREAS
•FORESTED AREAS
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CLOUDS AND THE ATMOSPHERE’S ALBEDO
•
The sun's rays are often siphoned out by clouds which reflect, scatter and
absorb a significant portion of the electromagnetic radiation incident (falling)
on them
•
Clouds are a major determinant of the weather and climate of equatorial
regions, keeping temperatures from being too high
•
(i)
Clouds are an important climatic resource as they:
produce precipitation (and freshwater);
(ii) act as reflective surfaces from the sun's rays;
(iii) absorb part of the sun's radiation;
(iv) protect the earth surface temperature from getting too hot;
(v) produce lightning (which is a form of electricity and fire source);
(vi) are a medium from which energy transfer takes place;
(vii) influence atmospheric humidity;
(viii) affect visibility (especially low clouds);
(ix) cleanse the air of pollutants; and
(x) are an indicator of weather (usually bad weather depending on the cloud
type); etc.
CLOUD ALBEDO FORCING
•
Cloud Albedo Forcing refers to an increase in albedo caused by
reflection of solar radiation by clouds (A)
CLOUD GREENHOUSE FORCING
•
Cloud Greenhouse Forcing refers to an increase in atmospheric
temperatures caused by absorption of solar radiation by clouds (B)
DAY
A
NIGHT
B
HIGH CLOUDS HAVE A NET GREENHOUSE FORCING &
ATMOSPHERIC WARMING EFFECT
(A): High clouds [ice-crystals cirrus clouds] transmit almost all of
insolation but absorb & delay outgoing longwave terrestrial
radiation, producing a net-warming effect
LOW CLOUDS HAVE A NET ALBEDO FORCING &
ATMOSPHERIC COOLING EFFECT
(B): Low clouds [thick stratus/cumulonimbus clouds] reflect most of
incoming shortwave & radiate longwave infrared to space, producing
a net-cooling effect
DAY
A
NIGHT
B
SCATTERING and DIFFUSE RADIATION
•Scattering – When insolation travels from space to the
earth’s surface (i.e. through the air), it encounters an
increasing density of atmospheric gases (remember air
pressure increases downwards or decreases upwards)
• When the insolation is absorbed by air molecules and then
re-emitted (i.e. passed through it) without altering its
wavelengths, scattering has occurred
• Scattering, however, will change the direction of the light
• Scattering is responsible for 7 % of Earth’s reflectivity or
Albedo
• Major atmospheric components responsible for scattering:
• Dust particles, pollutants, ice, cloud droplets & water
vapour
• The sky’s blue color is a result of scattering
WHY IS THE SKY BLUE ?
•SKY BLUE – is caused by scattering of visible light in the
blue wavelength (0.45 micron) because:
• 1881 – “Rayleigh Scattering” established the relationship
between wavelength of light to the size of molecules/particles
that cause the scattering:
• The shorter the wavelength, the greater the scattering
• The longer the wavelength, the less the scattering
• Thus, the shorter wavelengths of visible light (the blues &
violets) are scattered the most
• And since there are more BLUE than VIOLET wavelengths in
light, a blue sky prevails
WHY IS THE SKY AT SUNRISE & SUNSET RED ?
• SKY RED – is caused by scattering of visible light in the red
wavelength (0.71 micron) because:
• The angle of the sun’s rays is low on the horizon during
sunrise & sunset
• As a result, the rays have to pass through greater thickness
of the atmosphere (hence encounter more molecules [i.e.
more absorption] on its way to the observer)
• Hence, more of the sunlight is absorbed at sunrise &
sunset, leaving only the longer wavelengths of ORANGE &
RED to reach the observer
• In the lower atmosphere near the ground (i.e. near the
horizon), the atmospheric particles are mostly made up of
larger particles, which will absorb the blues & violets but
scatter the oranges & reds
DIFFUSE RADIATION
• DUE TO SCATTERING, SOME INCOMING INSOLATION IS
DIFFUSED BY CLOUDS AND ATMOSPHERE & TRANSMITTED
TO EARTH AS DIFFUSE RADIATION
• DIFFUSE RADIATION IS THE DOWNWARD COMPONENT OF
THE SCATTERED LIGHT
• DIFFUSE RADIATION IS LIGHT WHICH IS MULTIDIRECTIONAL
• HENCE, DIFFUSE RADIATION CASTS SHADOWLESS LIGHT
ON THE GROUND
DIRECT RADIATION
DIFFUSE RADIATION
ABSORPTION
• Absorption is the assimilation of radiation by molecules of matter in the
atmosphere (air molecules, gases, water vapour, cloud droplets,
pollutants, etc)
• Absorption involves the conversion of one form of energy to another
(e.g. from solar energy to sensible heat energy)
• If Earth’s albedo is 31 %, then insolation (both direct & diffuse) that is
not part of the 31 % reflected back into space will be absorbed (some in
the atmosphere & some on earth’s surface)
• Solar energy absorbed can either be converted into infrared radiation or
chemical energy (by plants via photosynthesis)
• During absorption, the temperature of the absorbing surface is raised –
that warmer surface will then radiate more total energy at shorter
wavelengths (the hotter the surface the shorter the wavelengths emitted)
• On the earth’s surface, total absorption by land & oceans add up to 45 %
of incoming insolation
• In the atmosphere, total absorption is about 24 % (mostly by clouds,
gases, dust & stratospheric ozone)
In the Stratosphere (Ozonosphere),
total absorption by Ozone of UVradiation is about 3 % of total solar
radiation received by the EarthAtmosphere System
CONDUCTION, CONVECTION & ADVECTION
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CONDUCTION is the molecule-to-molecule transfer of heat
energy as it diffuses through a substance
As molecules warm (get hotter), their vibration increases,
causing collisions that produce motion in neighboring
molecules, thus transferring heat from warmer to cooler
materials
Different materials of differing densities (gases, liquids &
solids) conduct sensible heat directionally from areas of higher
temperature to those of lower temperature
Conduction of heat (heat transfer) takes place at differing rates
depending on the conductivity of the material:
• Solids are better conductors of heat than liquids
• Liquids are better conductors than gases
• Land (Earth) is a better conductor than air (Atmosphere)
• Land (Earth) is a better conductor than water (Hydrosphere)
• Moist Air is a better conductor than Dry Air
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CONVECTION is the transfer of heat energy in the form of a
vertical motion, usually in the form of a loop or circle
In the atmosphere or bodies of water, warmer (less dense)
masses tend to rise and cooler (denser) masses tend to sink,
establishing CONVECTION
Convection is the dominant process in heat transfer in gases
(Atmosphere) and liquids (Hydrosphere) but is also present in
heat transfer from Earth’s Core to the Earth’s Crust
It is the convection of heat from Core (liquid) to Crust that fuels
Plate Tectonics and results in CONTINENTAL DRIFT
ADVECTION is similar to convection but proceeds at a
LATERAL direction rather than a vertical one.
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EXAMPLES OF CONDUCTION, CONVECTION & ADVECTION IN
THE NATURAL WORLD
CONDUCTION
•Surface Energy Budgets
•Temperature differences between land & sea
•The heating of land surfaces & overlying layers of air
•Differing Soil temperatures at differing layers
CONVECTION
•Atmospheric Circulation (air masses, winds, fronts, etc)
•Oceanic Circulation (ocean currents)
•Weather Systems
•Internal motions within Earth’s Core
ADVECTION
•Horizontal movement of winds – e.g. land & sea breeze
•Fog that moves from one area to another
•Local winds that blow from rural to urban areas
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ENERGY BALANCE IN THE TROPOSPEHERE
(i) Earth’s Radiation and the Greenhouse
Effect
(ii) Clouds and the Earth’s “Greenhouse”
(iii)Earth-Atmosphere Radiation Balance
DETAILS OF EARTH-ATMOSPHERE ENERGY BALANCE
Total lost by EarthAtmosphere=69
Total Albedo=31
Total
lost by
Atmos
=21
Total
Absorption=69
Total lost by
Stratosphere
=3
Total
lost
by
Earth=
45
ENERGY BUDGET BY LATITUDE &
TRANSFER OF HEAT
Clouds and the Earth’s “Greenhouse”
Cirrus clouds – 50 % Albedo & stops Longwave Radiation
from escaping into space
Cumulonimbus/Stratus clouds – 90 % Albedo & allows
Longwave Radiation to escape
HIGH CLOUDS – NET
GREENHOUSE FORCING &
ATMOSPHERIC WARMING :
[ice-crystals
DAYHigh clouds
NIGHT
cirrus clouds] transmit
almost all of insolation but
absorb & delay outgoing
longwave terrestrial
radiation, producing a netwarming
B effect
SOLAR ENERGY – ENERGY OF THE
FUTURE?
SOLAR ENERGY – ENERGY OF THE
FUTURE?
Firewood is no longer the
solution as forests are
depleted and land degraded
Kenyan women use solar panel
cookers which collect direct & diffuse
insolation through transparent glass or
plastic & trap infrared radiation in an
enclosed box or cooking bag (This is a
small-scale application of the Green
House Effect). Temperatures > 105 o C
(220 o F) can be used for baking,
purifying water & sterilizing
SOLAR OVENS – CHEF OF THE FUTURE?
•Solar ovens save energy, keep your kitchen more cool on hot days,
cook better tasting food, and make meals more fun. In remote areas, no
need to buy, collect, carry, and store fuel.
•No burned food, no smoke, no air pollution. Saves trees and soil, safe
around children. These durable and high quality models commonly reach
350 degrees F.
•Weighs 30 pounds and has an interior oven dimension of 14" x 14" x
10". Electric back-up fits on the glass and heats oven over 400 degrees F.
Even broils. Uses 500 watts at 117V AC - 1/7th the power of a
conventional oven. Black pot and thermometer make cooking fast and
easy.
•Model A Sun Oven (AA140) $229.00
•Electric back-up (AA139) coming soon (in development)
3 qt. black pot (AA146) $15.00
Thermometer (AA147) $5.00
SOLAR ENERGY – ENERGY OF THE FUTURE?
NREL Outdoor test
facility in Golden,
Colorado – a variety of
photovoltaic cell arrays
convert sunlight directly
into electricity
Kramer International
Solar Thermal Energy
installation, California
The Sacramento
Municipal Utility District
installed a PV array that
doubles as a parking lot
cover
Photovoltaic cells – The way to clean
energy and zero pollution?
SOLAR BATTERY – RECYCLEABLE,
REUSABLE & ENVIRONMENTALLY
FRIENDLY
THE SOLAR-POWERED CAR – NO LONGER A
DREAM BUT A REALITY & NECESSITY AS FOSSIL
FUELS RUN OUT
•CATCHING SOME RAYS: Solar vehicle team
member Lance Mobly (right) takes his turn in the
driver's seat of Aurora-II, during the car's unveiling
Tuesday.
•Aurora-II is the team's second sun-powered
vehicle, built to compete against other students'
solar-powered cars in a race from Indianapolis, Ind.
to Golden, Colo.
•Twenty University students have been
constructing the car for almost two years. "We
actually began designing this model in the middle
of the last race," Molby said. The race begins June
20.
SOLAR ROOF – GENERATES
ELECTRICTY & DOUBLES UP AS
PROTECTIVE ROOF (SAVES MONEY ON
ROOF TILES & UTILITY/POWER)
A SOLAR REMOTE HOUSE (VACATION
HOME) – 100 % DEPENDENT ON SOLAR
ENERGY FOR POWER (MOSTLY USED IN
SUMMER WHEN SUNSHINE IS
ABUNDANT)
SOLAR EFFICIENT HOUSE – HOUSE OF
THE FUTURE?
SOLAR VILLAGE/COMMUNITY – VILLAGE
OF THE FUTURE?
A SOLAR SIGN BOARD – 100 %
DEPENDENT ON SOLAR ENERGY FOR
POWER (SHINES EVEN AT NIGHT AS IT
USES VERY LITTLE POWER)
A SOLAR POWERED TRAFFIC LIGHTS –
USED IN REMOTE AREAS AND RURAL
VILLAGES
A SOLAR POWERED WATER WELL –
USED IN REMOTE AREAS AND RURAL
VILLAGES
SOLAR
PUMP
A SOLAR POWERED PORTABLE ELECTRICITY
GENERATOR – CAN BE USED ANYWHERE WHEN THE
SUN IS SHINNING
INSOLATION INDEX MAP OF THE UNITED
STATES – AN INDICATION OF SOLAR
ENERGY POTENTIALS
SOLAR COMPANIES & MULTINATIONALS –
THE LOGICAL & ETHICAL WAY FOR
SURVIVAL OF OIL COMPANIES IN THE
FUTURE?
END
THANK YOU