earth: a dynamic planet a solar and terrestrial...
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Solar and terrestrial radiation
Earth: A Dynamic Planet A
Solar and terrestrial radiation
AimsTo understand the basic energy forms and principles of energy transferTo understand the differences between short wave and long wave radiation.To appreciate that the wavelength of radiation impacts the interactions of energy with matter
Objectives• To identify basic forms of energy• To distinguish heat and temperature• To state three mechanisms of heat transfer• To define specific heat• To be able to state the first two laws of thermodynamics• To describe the electromagnetic spectrum• To define reflection, transmission, absorption and emission• To be able to state the basic electromagnetic radiation laws• To distinguish between solar and terrestrial radiation• To give a suitable definition for the solar constant and a currently accepted value• To define planetary albedo and explain its significance• To give values for the shortwave albedo for some surface types• To discuss the role of clouds• To list the most important radiation absorbing gases in the atmosphere and their
wavelengths of absorption
Earth: A Dynamic Planet A, Lecture 12
Solar and terrestrial radiation
Outline
Introduction• Solar radiation - the main energy supply to Earth
Energy and radiation• Energy, energy forms• Heat, temperature• Radiation• Reflection, albedo, absorption, transmission, emission
Laws of thermodynamics
Radiation laws I• Stefan-Boltzman law
The electromagnetic spectrum• Electromagnetic spectrum
Some properties of light• Diffuse light, scattering, refraction
Radiation laws II• Planck’s law• Wien's displacement law
Incoming solar radiation and its absorption• Spectrum• Albedo, Clouds, Planetary albedo• Solar radiation in the atmosphere
Emission and absorption of terrestrial radiation• Long wave radiation emission and absorption• The atmospheric window of longwave radiation• Venus and Mars
Earth: A Dynamic Planet
Earth: A Dynamic Planet A
Solar and terrestrial radiation
Topics• Basic energy forms, principles of energy transfer
• Wavelength of radiation.
• Interactions of radiation with matter
Outline
• Energy and radiation
• Laws of thermodynamics
• Radiation laws I
• The electromagnetic spectrum
• Some properties of light
• Emission, absorption, transmission
• Radiation laws II
• Incoming solar radiation and its absorption
• Emission and absorption of terrestrial radiation
Earth: A Dynamic Planet
Solar and terrestrial radiation
BulletsIntroduction• Solar radiation is the main energy supply for the Earth system• What is radiation? How does it interact with matter?• How is it distributed within the Earth system, in particular the atmosphere?Laws of thermodynamics• energy is the ability to do work• potential energy - energy due to position in a force field, e.g. water behind a dam, or
object at some height• kinetic energy - energy due to movement, weaker or harder collisions due to velocity• what is with a hot object?• internal energy of a macroscopic body - potential and kinetic energy of its molecules• heat is one way to change the internal energy of a body• temperature - “heat intensity” - average kinetic energy of the molecules• cup <-> bathtub• heat flux (an energy flux!) in direction of temperature difference• how does a car dashboard get hot? Radiation, another energy flux• radiation travels through vacuum, equally in all directions, intensity drops with the
square of the distance• mechanism how solar energy reaches Earth• objects can absorb radiation and heat up due do absorption• absorption increases kinetic energy of molecules• objects need to emit energy - otherwise they would heat up indefinitely• albedo, the reflectivity, is the fraction of radiation which is not absorbed• specific heat of matter, the amount of energy needed to heat up that matter by 1oK• water and soil have a very different specific heat - gives rise to local circulations - fog• 1. law of thermodynamics - absorbed energy by a body at rest is either used to do
external work or to increase the internal energy - total energy is conserved. • 2. law - heat flows occur along the temperature gradientThe electromagnetic spectrum• electromagnetic spectrum• wavelength, frequency• UV, visible light, PAR, infrared, ColorsSome properties of light• scattering - reflection of light in various directions from little objects (gases, aerosols)• diffuse light - direct light• scattering can be wavelength dependent• clouds - cloud droplets of about 20μm scatter all wavelengths of visible light more or
less equally -> clouds white• Mie scattering - equal scattering• air molecules are selective scatterers - oxygen and nitrogen scatter shorter wave-
lengths better than longer ones• blue sky is blue because blue is best scattered and thus comes from all directions• sunsets are reddish because most of the blue has been scattered away due to longer
atmospheric path• if the atmosphere contains many fine particles which are a little larger than the air
molecules (aerosols, e.g. SO2 from volcano eruptions), then the yellow light is scat-tered away, too, and the sunsets are even more red
Earth: A Dynamic Planet
Solar and terrestrial radiation
• Raleigh scattering - selective scattering• light bends (changes direction) if it enters another substance at an angle - refraction• twinkling or flickering of lights at a distance results from that effect - as the light has to
pass through various layers of air with different densities and the movement of air.Radiation laws II• blackbody - absorbs all incident radiation - a perfect absorber and emitter• Stefan-Boltzman law• all objects emit energy - the hotter the more• solar constant, temperature of the sun• Planck’s, Wien's displacement law
Incoming solar radiation and its absorption• at top of the atmosphere: 99% between 0.15μm and 4μm, 9%UV (λ<0.4μm), 49%
visible (0.8μm<λ<0.8μm), 42% infrared (λ>0.8μm)• comparison to blackbody radiator at ~6000oK• selective absorbers - absorb only at certain wavelengths O2, O3, H2O and CO2• glass - hot dashboard - green house• UV absorption within the atmosphere - O2 and O3 - of vital importance since they
absorb the high energy radiation from the sun which can do a lot of damage to life• Venus and Mars• planetary albedo, absorption by Earth, albedo of surface types• 30% of solar radiation reflected, 19% absorbed by atmosphere, 51% by surface
Emission and absorption of terrestrial radiation• heating of the lower atmosphere mainly through backradiation of Earth's surface and
absorption of long wave• hardly any heating of the troposphere by short wave• short wave <-> long wave• short wave albedo, long wave albedo• during days more sun light reflected from clouds - cooler• during nights more long wave radiation radiated back to the surface (water!) - warmer• the atmospheric window for longwave radiation• more CO2 might decrease long wave loss through the atmospheric window and thus
lead to a warmer atmosphere and consequently a warmer surface, too• delicate balance of absorption and emission maintains current climate; important to
understand it
Links• http://cwx.prenhall.com/bookbind/pubbooks/aguado2/chapter2/deluxe.html• Radiation laws: http://csep10.phys.utk.edu/astr162/lect/light/planck.html• Heat and Change of Phase: http://fermi.bgsu.edu/~stoner/p201/heat/• Heat Transfer http://fermi.bgsu.edu/~stoner/p201/transfer/• Ideal Gases http://fermi.bgsu.edu/~stoner/p201/idealg/index.htm
Earth: A Dynamic Planet
Solar and terrestrial radiation
GY1003 - Earth: A Dynamic Planet A, Lecture 12, Jörg Kaduk
n a force field
t
Solar and terrestrial radiation E
Earth: A Dynamic Planet
Energy and radiation
• Potential energy
• Kinetic energy
energy due to location i
energy due to movemen
p that matter by 1oK
atter
warm air/water.
due to potential and les of a body
Solar and terrestrial radiation
Gk
• Hot body?
• Heat - internal kinetic energy
• Temperature - average internal kinetic energy
Heat capacity of matter: energy needed to heat u
Heat transfer• Conduction: Heat flux due to direct contact of m
• Convection: Heat transport by water vapor and
Energy Sun -> Earth ?
internal energy: energy kinetic energy of molecu
Solar and terrestrial radiation
GY1k
Radiation
• another form of energy transfer
• travels through vacuum
• equally in all directions
• intensity drops with the square of the distance
• mechanism how solar energy reaches Earth
If radiation reaches a body it can be• reflected
• transmitted
• absorbed
matter
n
ic energy of molecules
Solar and terrestrial radiation
GY1
Interaction of radiation withReflection
albedo, the reflectivity, is the fraction of radiation which is reflected back
Transmission Radiation passes through the body without interaction
Absorption matter can absorb radiatio
heat up due do absorptionabsorption increases kinetEveryday example?
d to do external work
is conserved.
ed, only transformed.
. In a body of uniform
hange in temperature.
Solar and terrestrial radiation
GYk
Laws of thermodynamics
First lawEnergy absorbed by a body at rest is either use
or to increase the internal energy - total energy
Energy cannot be created nor can it be destroy
Second lawHeat never passes from a cooler to a hotter body
temperature there will never be a spontaneous c
o:
less it loses energy
on
y - otherwise itely
Solar and terrestrial radiation
Gk
Consequence
Earth receives Energy from the sun all the time, s
First law: Earth would heat up all the time un
Loss must be to space - only possible via radiati
Emissionobjects need to emit energthey would heat up indefin
the more
ls absorbed radiation
tion
mitter
d from the object
=5.67 x 10-8 Wm-2K-4
Solar and terrestrial radiation
Gk
Radiation laws I• Blackbody
Stefan-Boltzman law
All objects emit energy - the hotter
• radiative equilibrium temperature
temperature at which radiative energy loss equa
• absorbs all incident radia
• a perfect absorber and e
For a Black body
E=σT4
E energy flux (radiation) emitteT temperatureσ Stefan-Boltzmann Constant σ
transfers
tion
l energyd (1. Law)ork or to increase the
eating (1. Law)on - the hotter the morergy according to the
Solar and terrestrial radiation
GY1
Sum up I
• Conduction, convection and radiation are energy• Radiation travels through the vacuum• Reflection, transmission and absorption of radia• Heat is an expression of total internal energy• Temperature is an expression of average interna• Energy can only be transformed, never destroye• Absorbed energy is either used to do external w
internal energy (1. Law)• For a body at rest radiation absorption leads to h• All objects with positive temperature emit radiati• Black bodies - idealized absorbers - radiate ene
Stefan Boltzman Law• Do not confuse radiation, temperature and heat!
e?
Solar and terrestrial radiationk
Earth’s surface temperatur
5 min activity
Get together in groups of four
Assume: Radiation heating Earth, is 240 Wm-2.
Calculate the temperature of Earth.
Assume Earth behaves like a black body
ect I energy loss from Earthfer is through space.
radiation (since ):
σT4
1/4 K = 42.330.25 x 102 K
288oK! What’s wrong?nce!
on the wavelength - or n
Solar and terrestrial radiation
GY1
Solution: The greenhouse effAssume energy balance: energy input into earth =Input and loss are by radiation as the energy transNow one can use a law describing energy loss byinput=output and input and output are via radiation
Use Stefan Boltzmann law: E=
T = (E/σ)1/4
= (240Wm-2/(5.67 x 10-8 Wm-2K-4))1/4
= 240/(5.67 x 10-8)1/4 K = (240/5.67)1/4 x (1/10-8)
= 2.55 x 100 oK = 255oK
Much too cold! The observed temperature is aboutAtmosphere makes the differe
How? Interaction of radiation with matter depends“colour ” - of the radiatio
um
, F.K. and E.J. Tarbuck, 1998. The Atmosphere
hort-wave radiation
e light
Solar and terrestrial radiation
GY10k
The electromagnetic spectr
Source: Lutgens
long-wave radiation s
visibl
Spectrum
, F.K. and E.J. Tarbuck, 1998. The Atmosphere
Crest
Solar and terrestrial radiation
GY10k
Wave properties
Source: Lutgens
Frequency = 1/wavelength
WavelengthAmplitude
Trough
Viking 2 Lander image, NASA
Solar and terrestrial radiation
GY1
Sky of Mars
phere
ratories, 1965. Handbook of Geophysics and Space.
Solar and terrestrial radiation
GY
Solar spectrum at top of atmos
Source: Houghton, H.G., 1985. Physical Meteorology. After data from Air Force Cambridge Research Labo
5785 deg. K blackbody
Inte
nsity
Wave length (μm)
Earth’s surface
Gases are
selective
absorbers
Solar and terrestrial radiation
Gk
Solar spectrum at top of atmosphere and
Source: Peixoto, J.P. and A.H. Oort, 1992. Physics of Climate. After: Gast (1965)
c Radiation absorption
ward et al. (1955), Fels und Scharzkopf (1988)
errestrial,ong-wave
255oK
Solar and terrestrial radiation
GYk
Black Body curves of Sun and Earth - Atmospheri
Source: Peixoto, J.P. and A.H. Oort, 1992. Physics of Climate. After: Goody (1964), Ho
Wave length (μm)
solar,short-wave
tl
6000oK
of maximal emission
K
es”by a black body is:
, h=6.63x10-34 J s, nt, k=1.38x10-23 J K-1
ν
Solar and terrestrial radiation
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Radiation laws II
Wien's displacement law For a black body is the product of the wavelengthand temperature constant:
λmaxT = A = const = 2898 μm
Planck’s law - determines the “black body curvThe intensity of radiation of wavelength λ emitted
c speed of lighth Planck constantk Boltzman consta
The energy of light of frequency ν is given by: E=h
Bλ T( ) 2hc2
hvkT-------⎝ ⎠
⎛ ⎞ 1–exp--------------------------------------=
nge. An Earth System Perspective
its neighboursrth Mars
0.060 228
70 589
0 150 variable8 -56
5 -53
3 3
8 <2.51 <0.2536 >96-4-3 <0.0001
Solar and terrestrial radiation
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Venus and Mars
After: Graedel, T.E. and P.J. Crutzen, 1993. Atmospheric cha
Some physical properties of Earth and Property Venus Ea
Rel. mass of atmosphere 100 1
Distance from Sun (106km) 108 15
Solar constant (Wm-2) 2613 13
Albedo (%) 75 3Cloud cover (%) 100 5
Radiative temperature (oC) -39 -1
Surface temperature (oC) 427 1
Greenhouse effect (oC) 466 3
N2 (%) <2 7O2 (%) <1 ppmv 2CO2 (%) >98 0.0H2O (%) 1x10-4-0.3 4x10
transfers
he matter
; absorbed energy is internal energy (1. Law)
on - the hotter the more
n Boltzman Law
elength of the radiation
trial radiation -> warm-
Solar and terrestrial radiation
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Summary • Conduction, convection and radiation are energy
• Radiation travels through the vacuum
• Interaction of radiation with matter depends on t
• Energy can only be transformed, never destroyedeither used to do external work or to increase the
• All objects with positive temperature emit radiati
• Black bodies emit energy according to the Stefa
• Wavelength, frequency, colour, Wien’s law
• Interaction of radiation with matter depends on wav
• Gases are selective absorbers
• Atmosphere absorbs some solar but most terresing of the atmosphere - Greenhouse effect