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Geography and Environmental Studies 265 semester notes R120,00
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  5. Geography and Environmental Studies 265

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Geography and Environmental Studies 265 semester notes

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Summary of all work covered in the geo 265 module on atmospheric processes and climatology (lectures 2 - 33). This document includes notes from slides, lectures and the prescribed textbook, and has all the necessary graphs, tables and images. A list of topics covered can be seen on page one of the ...

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  • July 23, 2020
  • 125
  • 2019/2020
  • Class notes
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GEOGRAPHY AND ENVIRONMENTAL STUDIES 265: Lecture 2 – radiation, scattering, albedo and earth’s energy balance
Lecture 3 – the atmosphere: composition and structure
Lecture 4 – earth’s motions and Milankovitch cycles
Lecture 5 – energy, heat, heat transfer and temperature
Lecture 6 – energy absorption and distribution and basic pressure/temperature relationships
Lecture 7 – temperature distribution and controls
Lecture 8 – measuring temperature, heat stress and temperature hazards
Lecture 9 – water and the atmosphere
Lecture 10 – humidity and water vapour
Lecture 11 – adiabatic temperature change and vertical air movement
Lecture 12 – atmospheric instability
Lecture 13 – cloud formation and cloud types
Lecture 14 – fog formation and precipitation
Lecture 15 – atmospheric pressure and wind
Lecture 16 – upper air flow and surface winds
Lecture 17 – atmospheric circulation: localised circulation
Lecture 18 – global circulation processes
Lecture 19 – monsoons, westerly waves and jet streams
Lecture 20 – ocean-atmosphere coupling and ENSO
Lecture 21 – air mass formation and properties
Lecture 22 – mid-latitude cyclones and frontal systems
Lecture 23 – integrating air flow aloft and below
Lecture 24 – convective systems: thunderstorms
Lecture 25 – severe and supercell thunderstorms
Lecture 26 – tornadoes
Lecture 27 – tropical cyclones
Lecture 28 – the East-African wave and hurricane formation
Lecture 29 – extreme weather events
Lecture 30 – earth’s changing climate: natural variations
Lecture 31 – earth’s changing climate: anthropogenic forcing
Lecture 32 – climate projections and impacts of climate change
Lecture 33 – climate change adaptation




1

, LECTURE 2:
RADIATION, SCATTERING, ALBEDO AND EARTH’S ENERGY BALANCE

- All objects emit radiation as a function of their temperature
RADIATION:


- Radiation can travel through a vacuum
- The sun is the biggest source of energy to our planet; through radiation
- A perfect emitter (or black body) emits radiation proportional to the 4th power of its temperature
(Stephan-Boltzman Law)


STEPHAN–BOLTZMAN LAW: E = s T4
• E is the radiation emission from a body
• s is the Stephan-Boltzman constant equal to 5,67 x 10-8 W/m2 K4
• T is the temperature in Kelvin

Important note: the Stephan-Boltzman Law applies to perfect emitters only, which have an emissivity of 1. Other
bodies have an emissivity of less than 1.



Example question:

- A tungsten filament light bulb glows at a temperature of 2400K. Calculate how much energy the
lightbulb is giving off assuming an emissivity of 0.95

E = s T4
\ E = 4,67 x 10-8 x 2400 4 = 1 881 169 um
SOLUTION:




But a lightbulb is not a perfect emitter; it has an emissivity of 0,95.

\ E = 0,95 x 1 881 169 = 1 787 111, 42 um




The sun emits all wavelengths of radiation but not in equal amounts
Wien’s Law states that the wavelength of peak emission is dependent on the temperature of the object.



WIEN’S LAW: lmax = C/T
• C is a constant equal to 2898 um K
• T is the body’s temperature in Kelvin




2

,Example question:
- A giant star has a surface temperature of 20 000K. Calculate its wavelength of peak emission

lmax = C/T
\ lmax = 000 = 0,14 um




IMPORTANT LAWS OF RADIATION:
1. All objects continually emit radiation energy over a range of wavelengths (this includes cold objects)
2. Hotter objects radiate more total energy per unit area than colder ones
3. Hotter objects radiate more energy in the form of shortwave radiation than cooler objects
4. Objects that are good absorbers of radiation are also good emitters


EMISSIVITY:
- The relative ability of an object to emit energy by radiation
- It is the ratio of energy radiated by an object to the energy radiated by a black body at the same
temperature

𝐸 (𝑛𝑎𝑡𝑢𝑟𝑎𝑙 𝑜𝑏𝑗𝑒𝑐𝑡)
𝜀=
𝐸 (𝑏𝑙𝑎𝑐𝑘 𝑏𝑜𝑑𝑦)

- The emissivity of a black body would be equal to 1




EARTH’S EFFECTIVE TEMPERATURE:
Income radiation = outgoing radiation

- This is important because otherwise there would be an imbalance and earth’s average temperature
would constantly be getting hotter or colder.



ATMOSPHERIC INTERFERENCE:
When radiation strikes an object, three things may occur

1. Absorption: object absorbs the radiation energy, the molecules begin to move faster, and the
temperature increases.



3

, 2. Transmission: some energy passes through the object without being absorbed

3. Redirection: scattering and reflection




Scattering: light bounces back weaker and travels Reflection: light bounces back from the object at
in different directions the same angle and intensity
• Rayleigh scattering: Dominant backwards • Roughly 30% of insolation is reflected
(backscattering) and forwards – particle back into space (including backscattering)
size < 1/10 of wavelength
• Mie scattering: Omnidirectional scattering • Energy does not heat the earth or
of light – particle size roughly = atmosphere
wavelength (clouds) • Proportion of energy reflected is called
• Scattering explains how light reaches the albedo (α)
area in shadows or how a room is lit up • Earth’s albedo is due to clouds and the
during the day (diffused light) Earth’s surface




4

,LECTURE 3:
THE ATMOSPHERE – COMPOSITION AND STRUCTURE

The atmosphere: envelope of gases surrounding the geosphere, in which tiny solid and liquid particles are
suspended.

COMPOSITION OF THE ATMOSPHERE:
- The atmosphere consists of a mixture of discrete gases; each gas displays its own physical properties
and is available in different quantities
- The composition of air is not constant




GAS PERCENT
EARTH S MOST IMPORTANT




VOLUME
METEOROLOGICAL GASES:




Nitrogen 78%
Oxygen 20%
’ Water vapour 0 to 4%
Carbon dioxide < 0,1%
Methane < 0,1%
Ozone < 0,1%




EARTH’S EARLY ATMOSPHERE:
4,6 billion years ago, earth’s atmosphere was not the same as it is now

• Likely consisted of gases that were common to our solar system such as hydrogen, helium and carbon
dioxide
• Less dense gases (like helium) would have escaped Earth’s gravitational field which was too weak to
hold them
• The sun would have been particularly active and solar winds would have blown most gases into space

OUTGASSING à The release of gases from the earth’s core
- It was this process which generated the earth’s first enduring atmosphere
- Outgassing still occurs today; for example, gases are released from the core during volcanic eruptions




5

, IMPORTANT CONSTITUANTS OF OUR ATMOSPHERE:
o the movements of the atmosphere keep small solid and liquid particles in suspension in large quantities
AEROSOLS:




o microscopic particles include: seas salts, fine soil or dust, smoke, pollen, microorganisms
o aerosols are meterogically significant because they have reflecting properties and the acts as nuclei for
condensation
C A R B O N
D I O X I D E:




o Only presents as ± 391 parts per million in our atmosphere
o CO2 is an absorber of the energy emitted by earth; it thus influences the heating of the atmosphere
o The amount of carbon dioxide in our atmosphere has been rapidly increasing over the past century




o The amount of water vapour in the air varies significantly
V A P O U R :




o Water vapour is the source of all clouds and precipitation
W A T ER




o It is an important greenhouse gas
o When water undergoes a phase change, it absorbs or releases heat in the form of latent heat




o A form of oxygen which combines three atoms into each molecule (O3)
O Z O N E:




o The ozone layer is concentrated in the stratosphere
o Ozone absorbs the potentially harmful ultra-violet radiation from the sun and prevents it from reaching
the earth’s surface in large quantities
o Anything which reduces the amount of ozone in the atmosphere could potentially affect the well-being
of life on earth




OZONE DEPLETION:
CHLOROFLUOROCARBONS:

- In the past, CFCs were used in refrigerators, aircons and aerosol cans
- Favourable to use because they are odourless, stable, non-toxic (to humans) and inexpensive
- CFCs are chemically inactive in the lower atmosphere but not in the upper (stratosphere)

6

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