GEOGRAPHY 3015A

Atmospheric Scales The Boundary Layer
Vary in SPACE and TIME
The portion of the atmosphere influenced by the Earth’s surface over a time period of one day
MICRO 10 -2 to 10 3 m
Small-scale turbulence
Height: <100m to 2km
LOCAL 10 2 to 5x10 4 m
Small to large cumulus cloud
MESO 10 4 to 2x10 5
MACRO 10 5 to 10 8 m
Hurricanes, cyclones, jet stream
See Fig 1.1, p. 4 m
Thunderstorms/Local winds
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
See p. 5
Vertical
Extent

•
poorly understood near edge of atmosphere
We won’t concern ourselves with this scale in this course

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.
Absorption (absorptivity=

)
Results in conduction, convection and long-wave emission
2.
Transmission (transmissivity=

)
3.
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)
Water transmits solar energy and has a high heat capacity

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


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 =

(T
0
) 4
Radiant flux or flux density refers to the rate of flow of radiation per unit area (eg., W
 m -2 )
Irradiance = incident radiant flux density
Emittance = emitted radiant flux density

As the temperature of a body increases, so does the total energy and the proportion of shorter wavelengths
 max
= (2.88 x 10 -3 )/(T
0
) *wavelength in metres
Sun
 max
= 0.48
 m
Ultraviolet to infrared - 99% short-wave
(0.15 to 3.0
 m)
Earth
 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
H
2
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
Solar radiation
Microwaves are longest wavelengths used in remote sensing
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.

window absorption

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 = S i 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-

)

Field Research
Spatiotemporal patterns of plant ecophysiological stress in grassland, alpine krumholtz and riparian environments of southern Alberta
Measurements:
Microclimate stations (16)
Photosynthesis processes (LI-COR 6400XTR, TPS-1)
Fluorescence (FMS2, LI-COR 6400XTR)
Reflectance (Unispec-SC)
Sites:
Lakeview Ridge, Waterton Lakes National Park (PI=Letts)
Lethbridge Coulee Microclimate Station (PI=Letts)
Pearce Corners Cottonwood Grove (PI=Rood)
Helen Schuler Coulee Centre, Lori’s Island (PI=Letts)
Lethbridge Flux Station (PI=Flanagan)
Research Assistants: Kevin Nakonechny, Deborah Ball,
Clint Goodman, Leslee Shenton, Davin Johnson