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.

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?

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?)

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

…where σ = 5.67x10-8 Watts/(m2K4), E = Maximum rate of radiation emitted by each square meter of surface area, and T is the object’s ‘blackbody’ temperature in degrees Kelvin.

If some imaginary planet were to emit 500 Watts/ m2 of radiant energy, what would its blackbody temperature be?

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.

  1. (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?
  1. (3 pts.) What type of longwave radiation does the earth emit?
  1. (3 pts.) Does radiation emitted from the sun or the earth carry more energy per wave? Why?
  1. (5 pts.) Wien’s Law relates the peak wavelength of emitted light of an object to that object’s temperature:

λmax = 2897 / T

…where the numerator has units of μm · K and 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?

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.

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

Nebraska (for homework – 10 points): every 2C