One thing to keep in mind is that the sun shines only on one half of the globe,
ID: 2124622 • Letter: O
Question
One thing to keep in mind is that the sun shines only on one half of the globe, but the emission comes from all over the globe. Also, the 150 Wm^-2 from the atosphere will be all over the globe as well. This may help to get the 'right' result.
a) Determine the global average power density that the Earth's surface receives (ie., the total amount of sunlight falling on the Earth's
surface), and then calculate the amount absorbed by taking into account the Earth's albedo.
?e?Due to gases in the atmosphere approximately 150 Wm-2 is re-radiated back to the surface. Using the Stefan-Boltzmann expression, show that the global mean temperature of the earth
The Eart is 150 million km from the sun. The reflection from the Earth, clouds and atmosphere is 30% and the emissivity of the earth is approximately 0.6. The power density on the Earth's atmosphere is 1370 Wm^-2 (also known as the solar constant). One thing to keep in mind is that the sun shines only on one half of the globe, but the emission comes from all over the globe. Also, the 150 Wm^-2 from the atmosphere will be all over the globe as well. This may help to get the 'right' result. Determine the global average power density that the Earth's surface receives (ie., the total amount of sunlight falling on the Earth's surface), and then calculate the amount absorbed by taking into account the Earth's albedo. ?e?Due to gases in the atmosphere approximately 150 Wm-2 is re-radiated back to the surface. Using the Stefan-Boltzmann expression, show that the global mean temperature of the earth's surface is approximately 15oC. Why does this answer differ from part c)? (Hint you will need to recalculate the Power density to determine the amount of surface radiation before using the Stefan-Boltzmann equation) The radiation from the sun is given by Qr=Qsun/4piD^2 where D is the distance form the Sun. Venus is 108 million km from the Sun and has an albedo of 77%. Calculate Venus's steady state temperature. What are the reasons for the difference between the effective temperature of Venus and the effective temperature of Earth? (Venus's surface temperature is ~ 500 oC). Briefly describe the reasons for such a high effective temperature on Venus. Do you think this could happen to Earth?Explanation / Answer
a. total amount of sunlight falling on the earth surface = 1370 (1-0.3) Wm^2
= 479.5 Wm^2
given
The emissivity or reflectivity of the Earth is 0.6
so absorbed by the Earth. = 1- 0.6 = 0.4
0.4* 479.5 = 191.8 Wm^2
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