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 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 Extends to height of <100m to 2km 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 times the height of surface elements Highly irregular flow Laminar Boundary Layer Non-turbulent, ~ 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.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) 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 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’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)

Solar radiation Terrestrial radiation

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-  )