Agronomy 505 Homework Assignment 3
Due date: Thursday, October 10
(1) In this question, you will build upon your radiation model by adding one component of the surface energy balance for a leaf.
(a) This question is worth 3 points. Write a leaf surface energy balance equation that contains terms only for radiation balance and heat storage. If you use symbols that differ from what I have presented in class, you must define those symbols. I will take off points for incorrect use of symbols.
(b) This question is worth 3 points. Organize the leaf surface energy balance equation, so that it is a predictive equation for leaf temperature.
(c) This question is worth 2 points. Using the equation from part (b), generate a one-day simulation of leaf temperature during the summer solstice at 45oN. Please assume that the specific heat of the leaf is identical to that of water, and the leaf mass per area is 2 kg m-2. You will need to specify other parameters, including leaf temperature for outgoing longwave radiation. You must list these specifications.
(2) In this problem we are once again playing with an infrared thermometer. This time we have pointed it at the sky, and it reports a temperature of 20.3oC with an assigned emissivity e=0.95. There is a radiometer in close proximity that reports downward longwave radiation.
(a) This question is worth 2 points. On a clear sky day, the measurement from the radiometer is 331 W m-2. What is the clear sky emissivity on this day?
(b) This question is worth 2 points. On a cloudy day, the measurement from the radiometer is 406 W m-2. What is the cloudy sky emissivity on this day?
(3) A common saying among farmers is “a wet soil is a cold soil”.
(a) This question is worth 3 points. Use concepts from class lectures to scientifically interpret this saying. I am looking for accurate use of precise scientific vocabulary. You may use either English words or mathematical expressions or a combination of both.
(b) This question is worth 3 points. Rephrase your explanation such that the farmers, who have not taken this class or any science class beyond high school, may comprehend the physical mechanism of their saying.
(c) This question is worth 2 points. At what water content would you expect mineral soil to warm most rapidly? Use accurate and precise scientific vocabulary in your explanation.