1. Radiation
Mechanisms of Energy Transfer
Mass flux-
Energy flux-

2. Radiation: 1. Electromagnetic wave

3. Radiation: 2. particles (photons)
Photons have no mass, and travel at the speed of light
Energy of a photo
h= x10-34 m2 kg / s

4. Laws of blackbody radiation
1. Plank’s law
6000K
300K
2. Wien’s displacement law

5. Gray body:

6. Gray body:
Radiative equilibrium temperature

7. Absorbtivity
Reflectivity
Transmissivity

8. Surface
Remarks
Albedo = A
Emissivity
Soils
Dark, wet
Light, dry
Desert
Grass
Long (1.0 meters)
0.16-
0.90-
Short (0.2 meters)
0.26
0.95
Agricultural crops, tundra
Orchards
Forests
Deciduous (bare)
0.15-
0.97-
Deciduous (Leaved)
0.20
0.98
Coniferous
Water
Small Zenith angle
Large zenith angle
Snow
Old
0.40-
0.82-
Fresh
0.99
Ice
Sea
Glacier

9. What Happens to Incoming Solar Radiation
Selective absorption and emission of atmospheric gases
1. Energy level of atoms or molecules
Quantum jump: transition between different energy levels
2. Different energy form of a molecule or atom

10. Non-polar molecule does not have permanent dipole.
a. Rotational energy CO
Rotational energy transition can happen
as long as a photon’s wavelength is shorter than 1 cm, usually associated with microwave wavelength.
b. Vibrational energy
Polar molecule has
permanent dipole
Non-polar molecule does
not have permanent dipole.

11. Vibrational energy level transition
requires a photon's wavelength
shorter than 20 micrometer, usually
in the infrared band.
Vibration and rotation sometimes
combine together to form vibration-
rotation mode, the transition between vibration-rotation modes also
involves certain frequencies.

12. c. Photodissociation
Solar ultraviolet
photon
For photodissociation to occur, the wavelength of a photon must be in the ultraviolet band. To dissociate Oxygen the wavelength of radiation must be shorter than 200 nm.
Ozone is a loosely bonded molecule. To dissociate a Ozone molecule,
the frequency of a photon can be as low as 300 nm.

13. d. Electronic excitation
1st Shell
2nd Shell
Electrons may be excited from one shell to another shell by a photon with a
sufficiently high energy level. The wavelength is usually shorter than 1 micrometer.
e. Photoionization
To photoionize a molecule
requires the radiation with a
wavelength shorter than
100 nm.
Photoelectron

14. M What gases absorb shortwave radiation? Ozone
Photoionization
Electronic excitation
overlap
What gases absorb shortwave radiation?
Ozone
What gases absorb and emit longwave radiation?
Clouds
water vapor
CO2
Methane

15. Ozone 10-50 km (stratosphere) Formation of Ozone Sustaining Ozone
Depletion of Ozone

16. Ozone
Ozone Depletion
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

17. The Ozone Hole
Ozone concentration drops
sharply over Antarctica

18. The Ozone Hole 1. Polar winter leading to the stronger
circumpolar wind belt
(polar vortex) to isolate the cold air within it.
The
Ozone
Hole
Cold air
-80C
Polar vortex
2. As the cold temperatures persist over the polar, polar stratospheric clouds form.
3. Chlorine reservoir species HCl and ClONO2 become
very active on the surface of polar stratospheric clouds.

19. Atmospheric gases absorb all energy at wavelengths emitted from
surface except for 8-11 micron window known as Atmospheric
Window.
Oxygen, ozone, carbon dioxide, water vapor are great absorbers of IR radiation.

20. Trace gases, other important greenhouse gases
CFC-11
CFC-12
HCFC-22

21. Rayleigh Scattering The scattering from molecules
and very tiny particles (< 1 /10
wavelength) is predominantly
Rayleigh scattering.

22. Mie Scattering
The scattering from relatively large particles (> 1 wavelength)
is predominantly Mie scattering, which is not strongly wavelength dependent and produces a sharper and more intense forward lobe

23. Red Sunset

24. Making Radiation Measurements
There are three ways to make radiation measurements.
Thermal sensitive devise
Photoelectric cell (photodiode)
Photochemical sensor
What is the basic operating principle for the thermal devise?
How could we use a plate to measure broadband radiation?
Illuminate the surface with a bright light, or sun light…

25. 2. What besides radiation will affect temperature of the plate?
Convection and conduction
3. how could their effect on the temperature of the plate be removed?
Using a glass dome

26. What is the basic operating principle for the photoelectric cell?
A device that converts light into electricity.
Phototube is an electron tube in which electrons are excited and emitted by light. The simplest phototube is composed of a cathode coated with a photosensitive material. Light falling upon the cathode causes the liberation of electrons, which are then attracted to the positively charged anode, resulting in a flow of electrons (i.e., current) proportional to the intensity of the light.
Solid-state photodetector is the photoconductor whose resistance
changes when it is exposed to light. The solid-state photodetector
is small, inexpensive, and uses little power.

27. What is the basic operating principle for the photochemical sensor?
The photochemical sensor utilizes materials that tend to have
chemical reaction due to the absorption of light (including visible,
ultraviolet, and infrared). The light excites atoms and molecules
(shifts some of their electrons to a higher energy level) and thus
makes them more reactive. The bleaching of dyes or the yellowing
of paper by sunlight is a good example of photochemical reaction.
It is harnessed by plants in photosynthesis and by humans in
photography.
Broadband Radiation Instruments:
Shortwave K
Longwave L
Total Q = K + L

28. Upward stream and a downward stream of radiation
= -solar incident
= reflected solar
= emission from sun’s face
= emission from atmosphere
Net radiation
Spectral Radiation Instruments:

29. What are solar radiation measurements?
Direct (beam), diffused (sky), and global (total)

30. measures global-solar shortwave radiation
Pyranometer
measures global-solar shortwave radiation
Solar radiation curve outside atmosphere
Solar radiation curve at the sea level
Curve for balckbody at 50000K
Pyranometer sensor

31. Solar radiation irradiance measurements on a clear day

32. Shaded Pyranometer measures diffuse solar radiation
The pyranometer has a black thermopile sensor protected
by two concentric hemispherical optically ground covers. The
detector is independent of wavelength of radiation over the solar
energy spectrum. Both the pyranometer and the shading disk are
mounted on an automated solar tracker to ensure that the
pyranometer is continuously shaded.

33. Pyrometer — measures global longwave radiation
Fixed pyrometer
High speed pyrometer
Protable pyrometer
Video pyrometer

34. Pyrheliometer measures direct beam
used with a solar tracking system to keep the instrument aimed at the
sun. A pyrheliometer is used in the same setup with a pyranometer.

35. Pyrradiometer measures net radiation
For exact determination of
net radiation in short- and
longwave radiation range
(0.3 to >30 um) with two
separately working receivers.
The CN1-R Net Pyrradiometer
measures the net total radiation
flux (solar, terrestrial, and
atmospheric) downward and
upward through a horizontal
surface.