Solar Radiation Flashcards
What’s the position of the sun at (i) solar noon, (ii) sunrise and (iii) sunset
(i)
(ii)(iii) 0 degrees
What’s a black body emitter?
An object that absorbs all radiation falling on it, at all wavelengths. (source; wiki)
What’s the difference between solar spectra, black body, AM0, AM1.5
The solar spectrum is the range of electromagnetic radiation emitted by the sun, extending from ultraviolet to the infrared region.
AM0 and AM1.5 describe the pathlength of light through the atmosphere normalised to shorted possible path length.
AM1.5 has a tilted surface (37 degrees) with a zenith angle of 48 degrees.
What’s the difference between diffuse and direct radiation
Direct radiation is used to describe solar radiation travelling on a straight line from the sun down to the surface of the earth.
Diffuse radiation describes the sunlight that has been scattered by molecules and particles in the atmosphere but that has still made it down to the surface of the earth.
What are the three main trace gases responsible for absorption of infrared solar radiation in the Earth’s atmosphere?
H2O, 02, CO2
What layer in the Earth’s atmosphere absorbs UV radiation?
ozone layer (O3)
At what time of the day does the sun have an elevation angle of zero degrees?
sunset and sunrise
At what time of the day does the sun have a maximum altitude angle?
occurs at solar noon and depends on both latitude and declination angle:
In northern hemisphere:
alpha = 90deg + lat_angle - declination_angle
In southern hemisphere:
alpha = 90deg - lat_angle +-declination_angle
What’s the maximum altitude angle of the sun in KA on 21st of March?
alpha = 90 - 49 - 23.5
Which law describes the electromagnetic radiation emitted by a black body
Planck’s Law
Is a good absorber a good emitter or bad emitter?
a good emitter
What’s a zenith angle?
The zenith angle is the angle when the sun hits directly overhead AM=1
We’ve established that the solar radiation incident on Earth’s atmosphere is constant.
But hoe does the radiation on Earth’s surface vary?
- Atmospheric effects, including absorption and scattering
- Local variations in the atmosphere, such as water vapour, clouds and pollution.
- Latitude of the location
- Season of the year
- Time of the day
Describe the three events diffuse radiation goes through before reaching the earth
Scattering - due to particles in the atmosphere
Absorption - due to gases in the atmosphere
Reflection - from molecules, water droplets, ice crystals in high cloud, aerosols.
What’s the Azimuth angle
The compass direction from which the sunlight is coming
At solar noon, the sun is always:
- directly south in northern hemisphere
-directly north in the southern hemisphere
Why is the sky blue but sunset red?
When sunlight travels through the atmosphere, blue light scatters more than the other colours, leaving a dominant yellow-orange hue to the transmitted light.
The scatter lights makes the sky blue.
The transmitted light ultimately makes the sunset reddish orange.
