course on radiation and climate change...in climatology, only electromagnetic waves with wavelengths...
TRANSCRIPT
Course on radiation and climate change
• Lecturer: Martin Wild ([email protected]) (CHN L16.2) Will Ball ([email protected]) (CHN P14)
• Language: english
• Please everybody register (otherways no course infos, no grades)
• Copies of lecture slides will be provided
• Complementary practical work (computer lab, NO D39, 3 sessions), dates to be confirmed.
• Course Assistants: Laureline Hentgen ([email protected] ) (CHN L11) Christian Zeman ([email protected]) (CHN L16.3)
• The course takes place also on Friday 11.5. following ascension day (Auffahrt)
• 3 credit points
• Semester test for credit points (benotete Semsterleistung / graded semester performance):
Date of exam: 1.6.2017, written exam. Exam will cover material presented in lectures/exercises
• Website:
http://www.iac.ethz.ch/edu/courses/master/modules/radiation-and-climate-change.html
Website for this course
PDFs of slides available for download Further reading material is made available on the website
http://www.iac.ethz.ch/edu/courses/master/modules/radiation-and-climate-change.html
Introduction
Global Mean Energy Balance
Wild et al. 2013 IPCC AR5
Radiation and Climate Change FS 2018 Martin Wild
Radiation and climate change over Earth history
Radiation impacts climate evolution throughout Earth’s history
Radiation and Climate Change FS 2018 Martin Wild
Radiation and Climate Change FS 2018 Martin Wild
Why study radiation in the climate system?
• Radiation provides the energy for all climate processes as well as for the foundation of life on our planet
• The temporal and spatial variations in the radiation balance are the major determinants of the thermal and hydrological conditions on Earth, and the drivers of the atmospheric general circulation and the global water cycle
• Anthropogenic interference with the climate system occurs first of all though a perturbation of the radiation balance (e.g., greenhouse effect, air pollution, land use change)
• Radiation key driver of climate evolution over Earth history
• Practical application in the area of agriculture, tourism, renewable energy, solar power
Solar power production
Projected Use of Solar Power 21th Century
Radiation and Climate Change FS 2018 Martin Wild
source: German Advisory Council on Global Change
2000 2100
x 1
018 J
Source: Berner Fachhochschule Burgdorf
Insolation on horizontal and tilted (45°) panels 1992-2011
Measured at Burgdorf (Switzerland)
Tilted 45°South
Horizontal plane
Stability of solar energy source
Radiation and Climate Change FS 2018 Martin Wild
• Basic radiation laws and definitions • Sun-Earth relations • Radiative transfer trough the atmosphere and greenhouse
effect• Role of radiation in a hierarchy of climate models• Radiation and climate change over Earth’s History (faint Sun
paradox, Snowball Earth, Milankovich theory)• Present day radiation balance of the Earth (observations,
modeling approaches) surface, atmosphere, TOA• Anthropogenic perturbations of the Earth radiation balance
(greenhouse effect, global dimming)• Impacts of radiative changes on climate system components
Radiation and climate change: contents
Radiation and Climate Change FS 2018 Martin Wild
Radiation and Climate Change FS 2018 Martin Wild
Literature General overview: IPCC Reports, since 1990 (www.ipcc.ch) e.g. IPCC 5th assessment report (2013): Climate Change 2013: the physical science basis, Cambridge University Press.
5th IPCC assessment report (AR5):
Freely available on www.ipcc.ch
Radiation and Climate Change FS 2018 Martin Wild
Literature State of the art research is found in peer reviewed journals: Journals of major relevance for this course:
Radiation and Climate Change FS 2018 Martin Wild
Literature State of the art research is found in peer reviewed journals: Journals of major relevance for this course: J. Climate Bullletin of the American Meteorological Society J. Geophys. Res. Geophysical Research Letters ACP (Atmospheric Chemistery and Physics) A selection of relevant articles will be provided on the website
Radiation and Climate Change FS 2018 Martin Wild
1. Physical basis of radiation - terminoloy and definitions - basic radiation laws
Energy can be transported by electromagnetic radiation. Electromagnetic waves can be characterized by 3 parameters:
λ ν = c
λ : wavelength (m): distance between individual peaks in the oscillation. ν: frequency, units (s−1): number of oscillations that occur within a fixed (1 sec) period of time. c: speed of light (ms−1), constant in vacuum c = 299′792′458 ms−1. In climatology , sometimes wavenumbers rather than wavelengths are used: wavenumber (= 1/ λ): number of wave crests (or troughs) counted within a fixed length: Unit m-1
Radiation and Climate Change FS 2018 Martin Wild
Electromagnetic waves
Radiation can be described in terms of electromagnetic waves (classical physics), but also in terms of particles (photons) (quantum physics Einstein 1905) Energy per photon: E(ν)=hν The higher the frequency, the higher the energy of a photon
h=Planck constant, 6.62606957×10−34 J·s
ν = frequency (s-1) Energy per frequency interval dν: E(ν)=N(ν)hνdν
N(ν)=Number of photons per frequency Energy per frequency interval equals the number of photons times the energy per photon In climatology, only electromagnetic waves with wavelengths between about 0.1 µm and 100 µm (uv, visible light and infrared radiation) are relevant.
Radiation and Climate Change FS 2018 Martin Wild
Particle representation of radiation
Electromagnetic spectrum: classification of the electromagnetic waves according to their wavelengths:
In climatology, only electromagnetic waves with wavelengths between about 0.1 µm and 100 µm (uv, visible light and infrared radiation) are relevant.
Radiation and Climate Change FS 2018 Martin Wild
Electromagnetic spectrum
Terminologies and definitions
Radiation and Climate Change FS 2018 Martin Wild
Shortwave versus longwave radiation
Shortwave often known as solar
Longwave often known as thermal / terrestrial/ (far) infrared
Radiation and Climate Change FS 2018 Martin Wild
Terminologies and definitions
Separation according to wavelength
Ultraviolet (UV) radiation
q UV-C 0.20-0.28 µm (completely absorbed/scattered by O3) q UV-B 0.28-0.32 µm (genetic damage, dangerous for skin cancer)
q UV-A 0.32-0.40 µm (skin browning, strengthening of the immune system)
Visible radiation 0.40-0.74 µm
Near Infrared 0.74-4.0 µm
Far Infrared 4.0-100 µm (Longwave)
Radiation and Climate Change FS 2018 Martin Wild
Terminologies and definitions
Separation according to wavelength
Ultraviolet (UV) radiation
q UV-C 0.20-0.28 µm (completely absorbed/scattered by O3) q UV-B 0.28-0.32 µm (genetic damage, dangerous for skin cancer)
q UV-A 0.32-0.40 µm (skin browning, strengthening of the immune system)
Visible radiation 0.40-0.74 µm
Near Infrared 0.74-4.0 µm
Far Infrared 4.0-100 µm (Longwave)
Radiation and Climate Change FS 2018 Martin Wild
Source: Sun
Direct radiation Diffuse radiation
Reflected radiation
Global radiation=
sum of direct + diffuse
Separation according to origin shortwave (< 4 µm)
Terminologies and definitions
Radiation and Climate Change FS 2018 Martin Wild
Terminologies and definitions
Global, direct and diffuse radiation during a cloud-free day
Radiation and Climate Change FS 2018 Martin Wild
Terminologies and definitions
Direct and diffuse radiation during the course of a year
Site in Scotland Site in South Africa
60% diffuse 25% diffuse
Radiation and Climate Change FS 2018 Martin Wild
Measurements from Odessa, Ukraine
Global, direct and diffuse radiation over decades
Terminologies and definitions
Global
Direct
Diffuse
Radiation and Climate Change FS 2018 Martin Wild
Source: Earth surface + Atmosphere
Outgoing longwave radiation at TOA: Origin: Earth surface + Atmosphere
Surface downward longwave radiation
Origin: Atmosphere
Surface upward longwave radiation
Origin: Earth surface
Separation according to origin longwave (> 4 µm)
Terminologies and definitions
Radiation and Climate Change FS 2018 Martin Wild
Terminologies and definitions Outgoing longwave radiation at the Top of Atmosphere (TOA)
Radiation and Climate Change FS 2018 Martin Wild
Quantification of Radiation
Terminologies and definitions
Term Unit Description
Radiative energy J Energy Radiative flux W Power, Energy per time (J/s) Irradiance Wm-2 Power per Area Radiative emittance Wm-2 Power per Area
Radiance Wm-2sr-1
Power per Area per solid angle
Radiation and Climate Change FS 2018 Martin Wild
Irradiance (Bestrahlungsstärke) F
Total amount of radiative energy incident on a unit surface per unit time
Measured in units (Jm-2s-1) or (Wm-2) (Energy per square meter received
per second)
Similarly: Radiative Emittance: Total amount of radiation emitted from a
unit surface per unit time
Irradiance F = total radiative energyarea∗ time
=H
ΔAΔT
Terminologies and definitions
Radiation and Climate Change FS 2018 Martin Wild
Radiance (Strahldichte) I: Radiative flux from a specific direction and area on the celestial sphere
(cf. Irradiance: independent of direction of radiation)
Terminologies and definitions
• Direction defined by the angle θ between the direction to the source of the radiation and the vector normal to the surface
• If surface is horizontal: θ = Zenith angle
• Area defined as solid angle ω
Radiation and Climate Change FS 2018 Martin Wild
Solid angle ω (Raumwinkel)
Apparent area of a radiating element of the celestial sphere
The solid angle is equal to the area of a segment of a unit sphere surface of the unit sphere: 4π => ω = 2π for the half sphere visible above a given surface Unit: steradian sr-1 (dimensionless)
Terminologies and definitions
Radiation and Climate Change FS 2018 Martin Wild
Radiance (Strahldichte) I:
Units Wm-2sr-1
ΔFθ : potential irradiance, if the surface is oriented (with its normal vector)
towards the solid angle element from which the radiation is coming (surface optimally oriented towards the radiation source).
Terminologies and definitions
I = potential irradiancesolid angle
=ΔFθΔω
=ΔF
Δω cosθ
Radiation and Climate Change FS 2018 Martin Wild
From Radiance to Irradiance: Fraction of irradiance ΔF onto a surface coming from a specific solid angle element Δω, from a direction, defined by the angle θ.
Terminologies and definitions
ΔF = IΔω cosθ = Fθ cosθ Cosine law
If surface is horizontal: θ = zenith angle
Units Wm-2sr-1 (steradian). ΔFθ : potential irradiance ΔF: energy arriving on the surface in question (irradiance) I : Radiance
Zenith Angle and the cosine law
Zenith angle θ: angle between the vector normal to the horizontal surface and the vector pointing to the radiation source (e.g., sun).
Radiation and Climate Change FS 2018 Martin Wild
Fθ *A = F *B
with AB= cosθ
⇒ F = FθAB= Fθ cosθ
A
B Potential irradiance Fθ on the surface A equals Irradiance F on the horizontal surface B
Fθ
F θ
θ
Zenith Angle and the cosine law
Zenith angle θ: angle between the vector normal to the horizontal surface and the vector pointing to the radiation source (e.g., sun).
Radiation and Climate Change FS 2018 Martin Wild
A
B
Fθ Fθ cosθ
Irradiance F on horizontal surface: only vertical component of potential irradiance Fθ counts
Fθ *A = F *B
with AB= cosθ
⇒ F = FθAB= Fθ cosθ θ
Illustration of cosine law
Radiation and Climate Change FS 2018 Martin Wild
F = Fθ cosθ
Zenith angle Ɵ
Normal angle
Normal angle: angle between the vector normal to the illuminated surface, and the vector pointing to the radiation source (e.g., sun). Zenith angle special case of normal angle with horizontal surface
Radiation and Climate Change FS 2018 Martin Wild
Normal angle
(Cosine) Irradiance collector collects radiation from a 180°solid angle Pyranometer
Radiance collector collects radiation from a specified solid angle Pyrheliometer
Measuring irradiances and radiances
Radiation and Climate Change FS 2018 Martin Wild
Radiation and Climate Change FS 2018 Martin Wild
Measuring irradiances and radiances
Radiation and Climate Change FS 2018 Martin Wild
Measuring irradiances and radiances
Measurements from Mauna Loa Observatory Hawaii
Pyrheliometer
Pyranometer with shading disk
Radiation field with radiance distribution I(ϕ, θ) Dependent on: ϕ: Azimuth θ: Zenith angle
Radiation and Climate Change FS 2018 Martin Wild
Figure 1: Geometry of radiation fields and solid angles
Geometrical relations
Radiation and Climate Change FS 2018 Martin Wild
Definition Radiance: Fraction of irradiance dF onto a sensor surface dA coming from a specific solid angle element dω = dθ dΦsinθ is equal to
and thus from a given celestial area with a solid angle G and correspondingly from the half sphere above the sensor
Geometrical relations
dF = I(φ,θ )cosθdω = I(φ,θ )cosθ sinθdφdθ€
I =ΔFθΔω
=ΔF
Δω cosθ
€
FG = I(φ,θ)cosθ sinθdφdθG∫∫
FH = I(φ,θ )cosθ sinθ0
2π
∫0
π /2
∫ dφdθ = cosθ sinθ I(φ,θ )dφ0
2π
∫"
#$
%
&'
0
π /2
∫ dθ
Exercices 1) Calculate the total irradiance FH from the half sphere above a plane
for an isotropic radiance I(ϕ, θ) = I0.
2) What is the solid angle of the full lunar disk with an angular diameter of 0.5°?
Radiation and Climate Change FS 2018 Martin Wild
Geometrical relations