geography 3015a. atmospheric scales vary in space and time micro10 -2 to 10 3 m small-scale...
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GEOGRAPHY 3015A
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Atmospheric Scales
Vary in SPACE and TIME
MICRO 10-2 to 103 mSmall-scale turbulence
LOCAL 102 to 5x104 mSmall to large cumulus cloud
MESO 104 to 2x105 mThunderstorms/Local winds
MACRO 105 to 108 mHurricanes, cyclones, jet stream
The Boundary Layer
The portion of the atmosphereinfluenced by the Earth’s surfaceover a time period of one day
Height: <100m to 2km
Characteristics:Turbulence(i) frictional drag over surface(ii) convection
Variable height(i) diurnal heating(ii) large scale weather systemsaffect stabilitySee Fig 1.1, p. 4
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TroposphereExtends to limit of surface influence (~10km)
Atmospheric/Planetary Boundary Layer<100 m to 2km height (See previous page)
Turbulent Surface LayerIntense small-scale turbulence from convection and friction~ 50m by day, a few metres at night
Roughness LayerExtends to 1-3+ times the height of surface elementsHighly irregular flow
Laminar Boundary LayerNon-turbulent, ~ 0.1-5 mm layer adhering to surface Vertical
ExtentSee p. 5
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The Earth-Atmosphere System
First Law of ThermodynamicsEnergy can neither be created, nor destroyed
Energy Input = Energy Output + Energy Storage Change
The energy output is not necessarily in the same form as theenergy input
Modes of Energy Exchange in the Earth-Atmosphere System
1. Conduction2. Convection3. Radiation
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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°CForests 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
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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 bythe speed of light, divided by thewavelength
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
E = hv
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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 forunderstanding informationobtained in remote sensing
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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 flowof radiation per unit area (eg., Wm-2)
Irradiance = incident radiant flux densityEmittance = emitted radiant flux density
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Wien’s Displacement LawAs 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 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)
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Transmission through the Atmosphere
Radiation emitted from Earth is of a much longer wavelength and is ofmuch lesser energy
Some wavelengths of E-M energy are absorbed and scatteredmore efficiently thanothers
H2O, CO2, and ozone have the strongest absorption spectra
TransmissionLight moves through asurface (eg. on a naturalsurface)Wavelength dependent(eg. leaves)
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UV are shortestwavelengths practicalfor remote sensing
We are blind to everything except this narrow band
Microwaves are longestwavelengths used inremote sensing
Solarradiation
Terrestrialradiation
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Characteristic spectral responses of different surface types. Bands are thoseof the SPOT remote sensing satellite.
SpectralSignatures
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Atmospheric Windows
window
absorption
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Diffuse (D) and Direct (S) Solar Radiation
Clouds, water vapour, dust particles, salt crystals absorband 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, Kext reflected, absorbed and transmitted define atmospheric reflectivity, a, absorptivity, a, and transmissivity, a
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Diffuse Radiation
Measured using a shade disk
Radiation from entire sky except from within 3 of Sun
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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 thesurface (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- )
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FIeld ResearchSpatiotemporal patterns of plant ecophysiological stress in grassland, alpine krumholtz and riparian environments of southern Alberta
Measurements:Microclimate stations (16)Photosynthesis processes (TPS-1)Fluorescence (FMS2)Reflectance (Unispec-SC)
Sites:Lakeview Ridge, Waterton Lakes National Park (PI=Letts) Lethbridge Coulee Microclimate Station (PI=Letts)Pearce Corners Cottonwood Grove (PI=Rood)Lethbridge Flux Station (PI=Flanagan)
Research Assistants: Davin Johnson, Kevin Nakonechnyand Leslee Shenton
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Lakeview Ridge, Waterton Lakes National Park
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Lethbridge Coulee Microclimate Station
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Pearce Corners Cottonwood Grove,(PI=Stew Rood)
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Lethbridge Ecosystem Flux Site(PI = Larry Flanagan)