Microclimatology Flashcards
(17 cards)
How does the atmosphere modifies solar radiation?
Incoming short-wave solar radiation (K ↓) can be scattered, reflected or absorbed and re-emitted by particles in the atmosphere.
How and why does sky colouring occur?
The scattering of visible light (a type of solar radiation) causes colouring of the sky. If the radiation travels a short distance to an observer (i.e, is perpendicular to the Earth’s surface for example at midday) it be less scattered and the sky will appear blue and the sun whitish. If the radiation travels over a long distance (e.g at sunset) the sky appears reddish.
What are the absorption properties of the atmosphere?
The atmosphere is not a very good absorber of short wave radiation (0.15-3μm) but is a good absorber in the long-wave band (3-100μm). This is mainly caused by water vapour, carbon dioxide and ozone and within the atmospheric window of 8-11μm.
What are the three key equations governing radiative transfer?
Q* = K* + L* Net all wave radiation = net short-wave radiation + net long-wave radiation
K* = K↓ - K↑ Net short-wave radiation = Incoming short-wave radiation - outgoing short-wave radiation L* = L↓ - L↑ Net long-wave radiation = Incoming long-wave radiation - outgoing long-wave radiation
How is net all-type radiation (Q) measured?What are some of the difficulties associated with measurement in the field?
Q* is measured by a net pyrradiometer. It has 2 pyranometers and 2 pyrogeometers.
It is important to take into the sky view factor, the amount of sky that can be seen. Sky view factors affect the radiation balance and so surface and air temperatures. As a result, careful placement of instruments is required.
How is short-wave radiation (Q) measured?
By a pyranometer. It measures radiation of wavelengths 300-8000nm. It is important to take into the sky view factor, the amount of sky that can be seen.
Pyranometers have a:
- Glass dome - Black sensor
- White housing. - 180 degree view
Albedo can be measured by placing two pyranometers opposite one another; one facing up and one facing down.
How is long-wave radiation (Q) measured?
By pyrogeometers or by measuring surface/atmospheric temperature and using the Stefan-Boltzmann Law. They measure long-wave radiation and terrestrial irradiance of wavelengths 200nm to 100μm.
Pyrogeometers have a:
- Silicon dome - Black sensor
- White housing. - 180 degree view
What is the radiation budget over different surfaces at a diurnal scale?
Q* = (K↓ - K↑) + (L↓ - L↑)
The amount of outgoing solar/short-wave radiation and incoming and outgoing long-wave radiation can indicate different surfaces.
Radiation energy is . . .
Electromagnetic waves whose wavelength and magnitude depend on the temperature of the radiating body
Thermal energy can be in the form of ____ and ____
Sensible heat = can be felt and is a function of air temperature
Latent heat = is invisible to human senses and is proportional to the moisture content
A flux is . . .
The rate of flow of a quantity
Flux density is . . .
The flux of a quantity through unit surface area
Irradiance is . . .
Radiant flux density incident on the surface
Emittance is . . .
Radiant flux density emitted by a surface
Albedo is . . .
The ratio of incoming to outgoing radiation. It is the reflectance from the atmosphere and surface
Emissivity is . . .
The ratio of radiation emitted by a body compared to that of a perfect blackbody
Wein’s law states that . . .
The hotter a body the higher the frequency of radiation emitted
