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Geography And Environmental Studies 265 (GEO265)
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Geography 265
Semester 2 – Term 1
Week 1 – Lecture 1
The earth is made up of four distinct systems – The Biosphere, Geosphere, Hydrosphere and
Atmosphere – these systems interact with one another to make up the world we live in
The Geosphere
The land surface or solid earth (also called the lithosphere)
It is the largest sphere (6400km in depth)
It is divided into 4 components (Inner Core, Outer Core, Mantle and Crust)
The Hydrosphere
The is the water that we find on the planet, a dynamic mass of water that is constantly moving
The ocean is the main feature of the hydrosphere which covers 71% of earth’s surface with an
average depth of 3500m
It also includes underground water, clouds, rivers, lakes and glaciers and ice caps
The Biosphere
This is the organisms that live on earth from the trees to people to bacteria
Mainly found in a narrow belt closer to the earth’s surface
Sunlight plays a major role for organisms but some are able to adapt or have adapted to
extreme conditions
There are many interactions between the physical environment and that of organic life forms
The Atmosphere
This is a gaseous layer the surrounds the earth
99% of the atmosphere is found within 230km of earth’s surface
This layer provides rain, air, protection from radiation and redistributes heat energy from the
sun
The interaction of the Sun, the earth’s surface and the atmosphere are the cause of weather
Long term average patterns of weather is what we call climate
The atmosphere is not a blanket
The atmosphere is not like a greenhouse
Week 1 – Lecture 2 (47-)
Radiation, scattering, albedo and Earth’s energy balance
,Sun emits radiation energy onto earth and is very important for the climate and weather on earth
Radiation
All objects emit radiation as a function of their temperature
A perfect emitter (black body*) emits radiation proportional to the 4 th* of its temperature
(Stefan-Boltzmann law)
Hotter objects emit more energy and hotter objects emit shorter wave radiation
E∗¿ σT 4
E = the rate of radiation emission from a body
(Sigma) = (Stefan-Boltzmann constant) – 5.67 x 10 -8 W/m2K4
T = the temperature in Kelvin (-273.15 degrees C = 0K)
*NB* - Stefan-Boltzmann law = this law mathematically expresses the rate of radiation emitted per unit
area
Unlike sound, radiation is able to travel through a vacuum
The sun is the largest source of energy to earth
*NB* - A black body is an idealized physical body that absorbs all incident electromagnetic radiation,
regardless of frequency or angle of incidence
*NB* - It is a perfect emitter: at every frequency, it emits as much or more thermal radiative energy as
any other body at the exact same temperature
The sun emits electromagnetic radiation (energy) which travels at 299 792 458 m/s
Energy from the sun is transmitted as waves and travel in a straight lines (unless altered)
All wavelengths of radiation behave similarly thus, when an object absorbs radiation, there is an
increase in energy, which increases molecular motion (basically its temperature)
The sun emits all wavelengths but not in equal amounts (Wien’s Law states that the wavelength
of peak emission is dependent on the temperature of that object)
C
λ max ¿
T
C = Wien’s constant = 2898 μmK
T = Temperature (Kelvin)
,*NB* - Wien’s Displacement Law = describes mathematically the relationship between temperature of a
radiating body and its wavelength of max emission
Laws of Radiation
1. All objects continually emit radiant energy over a range of wavelengths
Thus, not only do hot objects such as the sun continually emit energy, but earth does as
well, even the polar ice caps
2. Hotter objects radiate more total energy per unit area than colder objects
The sun, which has a surface temperature of 6000K, emits about 160 000 times more
energy per unit area than the earth, which has an average surface temperature of 288K
3. Hotter objects radiate more energy in the form of short-wavelength radiation than cooler
objects do
We can visualize this law by imagining a piece of metal that, when heated sufficiently
produces a white glow. As it cools, the metal emits more of its energy in longer
wavelengths and glows a reddish color. Eventually, no light is given off, but if you place
your hand near the metal, the longer infrared radiation will be detectable as heat.
The Sun radiates maximum energy at 0.5 micrometer, which is in the visible range. The
maximum radiation emitted from earth occurs at wavelength of 10 micrometers, well
within the infrared (heat) range. Because the max earth radiation is roughly 20 times
longer than the max solar radiation, it is often referred to as long-wave radiation,
whereas solar radiation is called short-wave radiation (THIS LAW IS KNOWN AS WIEN’S
DISPLACEMENT LAW)
4. Objects that are good absorbers of radiation are also good emitters
Earth’s surface and the sun are nearly perfect radiators because they absorb and radiate
with nearly 100% efficiency. By contrast, the gases that compose our atmosphere are
selective absorbers and emitters of radiation. For some wavelengths the atmosphere is
nearly transparent (little radiation absorbed). For others, however, it is nearly opaque
(absorbs most of the radiation that strikes it). Experience tells us that the atmosphere is
quite transparent to visible light emitted by the sun because it readily reaches earth’s
surface.
Emissivity
o This is the relative ability of an object to emit energy by radiation
o Ratio of energy radiated by an object to the energy radiated by a black body at the exact same
temperature
E ( natural object )
ε=
E ( black body )
ε of a black body=I
, Atmospheric Interference
o When radiation strikes an object, 3 different things may occur simultaneously
1. Some energy may be absorbed
¬ The amount of energy absorbed by an object depends on the intensity of the radiation
and the objects ABSORPTIVITY. In the visible range, the degree of absorptivity is largely
responsible for the brightness of an object. Surfaces that are good absorbers of all
wavelengths of visible light appear black in color, whereas light-colored surfaces have a
much lower absorptivity.
2. Some energy may be transmitted
¬ Substances such as water and air, which are transparent to certain wavelengths of
radiation may simply transmit energy – allowing it to pass through without being
absorbed
3. Some energy may be reflected or scattered
¬ Some energy may “bounce off” the object without being absorbed or transmitted
In summary, radiation may be absorbed, transmitted or redirected, it depends greatly on the
wavelength of the radiation and the size and nature of the intervening material
Reflection and Scattering
o Reflection is the process whereby light bounces back from an object at the same angle and
intensity
o Roughly 30% of insolation is reflected back into space (including scattering)
o Energy does not heat the earth or the atmosphere
o Proportion of energy reflected is called albedo
o Earth’s albedo is due to clouds and the surface (e.g. water)
o Scattering produces a larger number of weaker rays, traveling in different directions, it disperses
light both forward and backward (back scattering)
o Rayleigh scattering – dominant backwards and forwards (particle size = < 1/10 of wavelength)
o Mie scattering – omnidirectional scattering of light (particle size = wavelength (clouds))
o Scattering explains how light reaches the area in shadow or how a room is lit up during the day
o Whether solar radiation is reflected or scattered depends largely on the size of the intervening
particles and the wavelength of the light
Reflection and Earth’s Albedo
About 30% of solar energy that reaches our planet is reflected back to space, this energy is lost
to earth and does not play a role in heating the atmosphere or earth’s surface
The fraction that is reflected by an object is called ALBEDO
The albedo for earth as a whole (planetary albedo) is 30%, the amount of light reflected from
earth’s land-sea surface represents only about 5% of the total planetary albedo
Scattering and Diffused Light
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