GEOGRAPHY 3015A
IT WAS AN INTERESTING SUMMER!
2 hours after the Lethbridge tornado
IT WAS A TRAGIC SUMMER
Atmospheric Scales
Vary in SPACE and TIME
MICRO
10-2 to 103 m
Small-scale turbulence
The Boundary Layer
The portion of the atmosphere
influenced by the Earth’s surface
over a time period of one day
Extends to height of <100m to 2km
LOCAL
102 to 5x104 m
Small to large cumulus cloud
MESO
104 to 2x105 m
Thunderstorms/Local winds
MACRO
105 to 108 m
Hurricanes, cyclones, jet stream
Characteristics:
Turbulence
(i)
frictional drag over surface
(ii)
convection
Variable height
(i)
diurnal heating
(ii)
large scale weather systems
affect stability
Troposphere
Extends to limit of surface influence (~10km)
Atmospheric/Planetary Boundary Layer
<100 m to 2km height (See previous page)
Turbulent Surface Layer
Intense small-scale turbulence from convection and friction
~ 50m by day, a few metres at night
Roughness Layer
Extends to 1-3+ times the height of surface elements
Highly irregular flow
Laminar Boundary Layer
Non-turbulent, ~ 0.1-5 mm layer adhering to surface
Vertical
Extent
The Earth-Atmosphere System
First Law of Thermodynamics
Energy can neither be created, nor destroyed
Energy Input = Energy Output + Energy Storage Change
The energy output is not necessarily in the same form as the
energy input
Modes of Energy Exchange in the Earth-Atmosphere System
1.
2.
3.
Conduction
Convection
Radiation
What happens to solar energy ?
1.
2.
3.
Absorption (absorptivity=)
Results in conduction, convection
and long-wave emission
Transmission (transmissivity=)
Reflection (reflectivity=)
 +   +  = 1
The response varies with the surface type:
Snow reflects 40 to 95% of solar energy and requires a
phase change to increase above 0°C
Forests and oceans absorb more than dry lands (later we’ll see
why dry lands still “heat up” more during the day)
Oceans transmit solar energy and have a high heat capacity
Characteristics of Radiation
Energy due to rapid oscillations of electromagnetic
fields, transferred by photons
The energy of a photon is equal to
Planck’s constant, multiplied by
the speed of light, divided by the
wavelength
E = hv

All bodies above 0 K emit radiation
Black body emits maximum possible radiation per unit area.
Emissivity,  = 1.0
All bodies have an emissivity between 0 and 1
Electromagnetic Radiation
Consists of electrical field
(E) and magnetic field (M)
Travels at speed of light (C)
The shorter the wavelength,
the higher the frequency
This is important for
understanding information
obtained in remote sensing
Temperature determines E,  emitted
Higher frequencies (shorter wavelengths) are
emitted from bodies at a higher temperature
Max Planck determined a characteristic
emission curve whose shape is retained for
radiation at 6000 K (Sun) and 288 K (Earth)
Energy emitted = (T0)4
Radiant flux or flux density refers to the rate of flow
of radiation per unit area (eg., Wm-2)
Irradiance =
Emittance =
incident radiant flux density
emitted radiant flux density
Wien’s Displacement Law
As the temperature of a body increases, so does the
total energy and the proportion of shorter wavelengths
max = (2.88 x 10-3)/(T0)
*wavelength in metres
Sun’s max = 0.48 m
Ultraviolet to infrared - 99% short-wave (0.15 to 3.0 m)
Earth’s max = 10 m
Infrared - 99% longwave (3.0 to 100 m)
Transmission through the Atmosphere
Some wavelengths of
E-M energy are
absorbed and scattered
more efficiently than
others
H2 O, CO 2, and ozone
have the strongest
absorption spectra
Transmission
Light moves through a
surface (eg. on a natural
surface)
Wavelength dependent
(eg. leaves)
Radiation emitted from Earth is of
a much longer wavelength and is of
much lesser energy
Terrestrial
radiation
Microwaves are longest
wavelengths used in
remote sensing
Solar
radiation
We are blind to
everything except
this narrow band
UV are shortest
wavelengths practical
for remote sensing
Characteristic spectral responses of different surface types. Bands are those
of the SPOT remote sensing satellite.
Atmospheric Windows
In the diagram below, peaks are windows, while troughs
identify wavelengths that are heavily absorbed
WINDOWS
ABSORPTION
Diffuse (D) and Direct (S) Solar Radiation
Clouds, water vapour, dust particles, salt crystals absorb
and reflect some of the incoming solar radiation (K).
Most is transmitted through clear skies (S) but some is
scattered, resulting in a diffuse component (D)
Clouds are very effective at scattering, resulting in D.
The proportion of extraterrestrial radiation, Kext reflected,
absorbed and transmitted define atmospheric reflectivity, a,
absorptivity, a, and transmissivity, a
Diffuse Radiation
Measured using a
shade disk
Radiation from entire
sky except from within
3 of Sun
S is weaker when the zenith angle is large
S = Si cos Z
Why ? The beam is simply spread out over a
larger area (Figure 1.7, p. 15)
The total short-wave radiation received at the
surface (K) is defined as:
K = S + D
A proportion is reflected: K =   K
Net short-wave radiation, K*, is defined as follows:
K* = K - K
OR
K* = K (1- )