Quiz #3 Study Guide Pt. 1


Radiative equilibrium (5 pts).  Energy balance. Incoming radiant energy (sunlight) is balanced by an equal amount of (but not necessarily the same kind of) outgoing radiant energy, temperature remains constant.

Filtering effect of the atmosphere (10 pts).  Does the atmosphere mostly absorb, selectively absorb, or mostly transmit UV, VIS, and IR radiation? What gases are important in each case? What does the term window mean? What property makes water vapor, carbon dioxide, methane, etc. greenhouse gases?

Greenhouse effect (simplified view) (15 pts).  With an atmosphere (containing greenhouse gases), the temperature of the earth's surface is warmer than it would be without an atmosphere. H2O, CO2, and other greenhouse gases selectively absorb IR radiation. The atmosphere in turn radiates IR radiation into space and back toward the ground. How is it possible for the earth's surface to radiate away more energy than it receives from the sun and still be in energy balance?  What effects do clouds have on nighttime and daytime temperatures? Why?

Earth-atmosphere energy budget (10 pts).  Two relatively easy questions: (i) What percentage of the sunlight arriving at the top of the atmosphere reaches the ground and is absorbed? (ii) What happens to the remaining sunlight? These next questions are a little harder: (i) Why do lower parts of the atmosphere emit more energy downward toward the ground than upward into space?  (ii) How is it possible for the earth's surface to emit more radiant energy than it gets from the sun?  (iii) On average does the earth's surface get more radiant energy from the sun or from the atmosphere?  How could you explain that?

Sample Questions (from the online quiz packet)
Quiz #2: 2, 5, 7, 8, 12a,b,&c          Final Exam: 20       and Questions 1, 4, 9, 11, 13, 14, and 16 from this Set of Sample Questions

 Humidity variables (35 pts).  Ways of measuring or specifying the amount of water vapor in the air.
mixing ratio (r) - the actual amount of water vapor in air expressed as grams of water vapor per kilogram of dry air (think about what the units mean). This variable is not affected by changes in air temperature (unless you cool air below its dew point temperature) or pressure, it changes only when water vapor is added to or removed from the air.

saturation mixing ratio (rs) - the water vapor capacity of the air in grams of water vapor per kilogram of air. This property of air depends on temperature; you can look the value of rs in a chart or on a graph.

Saturation is an upper limit to the amount of water vapor that can be found in the air. The saturation mixing ratio is a property of air and depends on the air temperature - there can be a lot more water vapor in warm air than in cold air. When air is saturated with water vapor, RH = 100% and condensation balances evaporation.

relative humidity (RH) - the amount of water vapor expressed as a percentage of the maximum amount (the saturation amount):
RH = 100% x r /rs
RH does not really tell you how much water vapor is in the air. The saturation amount, rs, depends on the air temperature and you may not know what that is. How can you change the RH? How would you expect the RH to change during the day?

dew point temperature (Td) - the temperature to which you must cool air in order for it to become saturated (RH becomes 100%). If you know Td, you can determine the mixing ratio (and vice versa), thus Td is a good measure of the actual amount of water vapor in the air. A large difference between the air temperature and the dew point temperature means the relative humidity is low. What is the RH when the difference is small? When the difference is zero?  Click here if you want to review this material on humidity variables.  Here is a reasonably challenging humidity variable question.

Miscellaneous (25 pts). Cooling moist air to below its dew point and then warming it back up. Rain shadow effect. Why is the relative humidity indoors often very low in the wintertime (where did that indoors air originate, did that air contain a lot, or not so much water vapor)? Measuring relative humidity and dew point with a sling psychrometer. Dry and wet bulb temperatures. Heat index.  What role do cloud condensation nuclei (particles) play in cloud formation.  Cloud in a bottle demonstration.  Here's another pretty tough question.

Sample Questions
Quiz #3: 3, 12, EC1 and EC3          Final Exam: 1, 49