GEOGRAPHY 3015A

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

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

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

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

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

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

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

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)

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)

UV are shortestwavelengths practicalfor remote sensing

We are blind to everything except this narrow band

Microwaves are longestwavelengths used inremote sensing

Solarradiation

Terrestrialradiation

Characteristic spectral responses of different surface types. Bands are thoseof the SPOT remote sensing satellite.

SpectralSignatures

Atmospheric Windows

window

absorption

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

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 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- )

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

Lakeview Ridge, Waterton Lakes National Park

Lethbridge Coulee Microclimate Station

Pearce Corners Cottonwood Grove,(PI=Stew Rood)

Lethbridge Ecosystem Flux Site(PI = Larry Flanagan)