GEOGRAPHY 3015A

Atmospheric Scales Vary in SPACE and TIME MICRO10 -2 to 10 3 m Small-scale turbulence LOCAL10 2 to 5x10 4 m Small to large cumulus cloud MESO10 4 to 2x10 5 m Thunderstorms/Local winds MACRO10 5 to 10 8 m Hurricanes, cyclones, jet stream The Boundary Layer The portion of the atmosphere influenced by the Earth’s surface over 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 systems affect stability See Fig 1.1, p. 4

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 times the height of surface elements Highly irregular flow Laminar Boundary Layer Non-turbulent, ~ mm layer adhering to surface Vertical Extent See p. 5

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.Conduction 2.Convection 3.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

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 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

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 =  (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

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 )/(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)

Solar radiation Terrestrial radiation

Spectral Signatures

Atmospheric Windows window 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 = 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  ORK* = 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 (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 Nakonechny and 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)