ATS 351, Spring 2010 Lab #2 Energy & Radiation 60 points Please show your work for calculations Question #1: Energy (11 points) Heat is a measure of the transfer of energy from a body with a higher temperature to a body with a lower temperature. There are three types of heat transfer: 1. Conduction 2. Convection 3. Radiation The formation of a thunderstorm on a hot, sunny summer day is a great way to illustrate the transfer of heat by all three mechanisms: 1. First, electromagnetic waves from the sun travel through the atmosphere and heat the soil and vegetation molecules at the surface of the earth. 2. The excited molecules at the surface then transfer their energy to adjacent air molecules in the atmosphere, thus heating the lower atmosphere. 3. Since warm air is LESS dense than cold air, the warm air parcel at the surface will rise to replace colder air aloft. A.(3 pts) On the diagram below, please fill in the blanks with Conduction, Convection, or Radiation, corresponding to the descriptions of how heat is transferred at points 1, 2 & 3. Radiation Convection Conduction
B. (4 pts) Warm air rises because it is less dense than cold air. As this warm air rises, the water vapor it contains condenses, forming liquid cloud droplets and eventually rain. Warm air that rises establishes updrafts, which sustain thunderstorms. Recalling your knowledge of latent heat from the lab presentation, why does the air within the storm cloud remain warm, sustaining updrafts? During condensation, latent heat is released to the atmosphere, warming the air. This helps the air remain warmer than the surrounding air, so it continues to rise. C. (4 pts.) Often, if a storm cloud begins to rain, the storm will die. Again, recalling your knowledge of latent heat, explain why the evaporation of rain below the cloud would suppress the storm? (Hint: What drives updrafts that sustain thunderstorms?) The process of evaporation requires taking latent heat from the environment and therefore it is a cooling process. Since storms are driven by warm, sustaining updrafts from buoyant parcels, cooling the air by evaporation would act against convection and suppress the storm. Question #2: Blackbody Temperature (10 points) All things emit radiation. As the temperature of an object increases, more total radiation is emitted each second. The Stefan-Boltzmann Law expresses this mathematically: E =σ T4-8 2 4 where σ = 5.67x10 Watts/(m K ), E = Maximum rate of radiation emitted by each square meter of surface area, and T is the object s blackbody temperature in degrees Kelvin. 2 If some imaginary planet were to emit 500 Watts/ m of radiant energy, what would its blackbody temperature be? E= σ T4 1 E 4 E E T4 = T =4 T = σ σ σ 1 4 W 500 2 m = 306.4[ K ] T= 8 W 5.67 x10 2 4 m K
Question #3: Electromagnetic Spectrum (14 points) Pictured below is the electromagnetic spectrum. The electromagnetic spectrum characterizes radiation by wavelength. As the wavelength of light decreases, the energy carried per wave increases. The sun radiates light in the shortwave (SW) part of the spectrum, at wavelengths between 0.4 and 0.7 μm, while the earth radiates light in the longwave (LW), between 5 and 25 μm. A. (3 pts.) Recalling that 1 micron (μm) = 1.0 * 10-6 meters (m), and using both of the above diagrams, what type (i.e. visible, infrared, ultraviolet, microwave) of shortwave radiation does the sun emit? The sun emits visible radiation. B. (3 pts.) What type of longwave radiation does the earth emit?
The earth emits infrared radiation. C. (3 pts.) Does radiation emitted from the sun or the earth carry more energy per wave? Why? Shorter wavelengths carry more energy per wave. Therefore, the sun s radiation carries more energy because it emits at shorter wavelengths than the earth. D. (5 pts.) Wien s Law relates the peak wavelength of emitted light of an object to that object s temperature: 2897[µm K ] T λmax = where T is in degrees Kelvin. Using your answer from Question 1, what would you expect the peak wavelength of light (in microns) of radiation emitted by this imaginary planet to be? T = 280.3 K (from question 1) λmax = 2897[ µm K ] = 9.45[ µm] 306.4[ K ] Question #4: Short Answers (15 points) Using the information provided in our first lecture and in Appendix B in the book, look at the surface plot image below and state what conditions (temp, dewpoint, wind, pressure, weather) are indicated at stations marked CAO, ALS and COS.
CAO Temp = 23 F Dewpoint = 16 F Wind = NNE, 20 kt Pressure = 1024.2 Weather = light snow ALS Temp = 25 F Dewpoint = 23 F Wind = NNW, 5 kt Pressure = 1021.1 Weather = light snow COS Temp = 21 F Dewpoint = 20 F Wind = S, 10 kt Pressure =1028.3 mb Weather = fog
Question #5: Surface Analysis (10 points) Draw temperature contours (isotherms) on the surface analysis maps with the specified contour interval. Wyoming (in class no points): every 5 C HAVE TO DO
Nebraska (for homework 10 points): every 2 C HAVE TO DO