--> DUE in class on Wednesday, January 18 at 10:30 am You may handwrite your answers, but please write neatly and large enough so we can read it. 1. Compute the effective radiating temperature TE for Venus using the equation for planetary energy balance: S(1-A) / 4 = sigma TE4. On Venus the average solar flux over the surface is S=661 W/m2 and the albedo A = 0.8 (sigma = 5.67 X 10 -8 W/m2/K4 for all planets). (Remember you can compute a number to the 1/4 power by taking its square root twice.) How does your answer for TE compare to the actual average surface temperature, which is 753 K? 2. Use the inverse-square law (see Fig 3-5) to compute the solar energy flux at the distance RE from the sun. The solar flux at the surface of the sun is about 63,000,000 W/m2 and the radius of the sun is 696,000 km. The Earth-sun distance RE is 149,598,000 km. 3. Describe the greenhouse effect as if to a friend in about 50 words. 4. If the albedo of a cloudy sky is Ac and the albedo of the surface is As, then the fraction of absorbed radiation by the planet is (1-A)=(1-As)(1-Ac). a) Compute A if As = 0.2 and Ac = 0.7 b) Compute A if As = 0.7 and Ac = 0.7 c) Use this calculation to explain that adding clouds over a darker surface affects the planetary albedo more than adding clouds over a lighter surface. 5. a) During the polar winter (total darkness for several months), what is the effect on surface temperature if a low cloud is added versus when a high cloud is added to an otherwise cloud-free atmosphere? b) Repeat this question for polar summer (24 hour sunlight for several months). Explain if there are competing effect in this case. |