Solar Radiation

Question 1

What’s the position of the sun at (i) solar noon, (ii) sunrise and (iii) sunset

Answer 1

(i)
(ii)(iii) 0 degrees

Question 2

What’s a black body emitter?

Answer 2

An object that absorbs all radiation falling on it, at all wavelengths. (source; wiki)

Question 3

What’s the difference between solar spectra, black body, AM0, AM1.5

Answer 3

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.

Question 4

What’s the difference between diffuse and direct radiation

Answer 4

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.

Question 5

What are the three main trace gases responsible for absorption of infrared solar radiation in the Earth’s atmosphere?

Answer 5

H2O, 02, CO2

Question 6

What layer in the Earth’s atmosphere absorbs UV radiation?

Answer 6

ozone layer (O3)

Question 7

At what time of the day does the sun have an elevation angle of zero degrees?

Answer 7

sunset and sunrise

Question 8

At what time of the day does the sun have a maximum altitude angle?

Answer 8

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

Question 9

What’s the maximum altitude angle of the sun in KA on 21st of March?

Answer 9

alpha = 90 - 49 - 23.5

Question 10

Which law describes the electromagnetic radiation emitted by a black body

Answer 10

Planck’s Law

Question 11

Is a good absorber a good emitter or bad emitter?

Answer 11

a good emitter

Question 12

What’s a zenith angle?

Answer 12

The zenith angle is the angle when the sun hits directly overhead AM=1

Question 13

We’ve established that the solar radiation incident on Earth’s atmosphere is constant.

But hoe does the radiation on Earth’s surface vary?

Answer 13

1. Atmospheric effects, including absorption and scattering
2. Local variations in the atmosphere, such as water vapour, clouds and pollution.
3. Latitude of the location
4. Season of the year
5. Time of the day

Question 14

Describe the three events diffuse radiation goes through before reaching the earth

Answer 14

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.

Question 15

What’s the Azimuth angle

Answer 15

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

Question 16

Why is the sky blue but sunset red?

Answer 16

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.