Quiz #3 Study Guide

Humidity variables (35 to 40 pts).  Water vapor in the atmosphere.
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 to review this material on humidity variables.  Here is a reasonably challenging humidity variable question.

Miscellaneous (30 to 35 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. 

Sample Questions (from the online quiz packet)
Quiz #3: 3, 12, EC1 and EC3          Final Exam: 1, 49       

Cloud identification and classification (45 pts). Ten cloud types. Clouds are classified according to altitude and appearance; what key words are used? You should be able to identify each of the 10 cloud types from pictures (hand drawn) or from a written description (eg. high altitude cloud with a filamentary appearance). How would you distinguish between Cc, Ac, and Sc or between Cs and As? What cloud type could produce a halo? Common features on thunderstorm clouds: anvil, mammatus, shelf cloud.  Here's a link to the hand drawn cloud chart shown in class (abbreviations are used instead of the full cloud names)

Sample Questions      Quiz #4: 1,4,10,EC2   Final Exam: 8,44

 Formation of precipitation (20 pts). Approximate sizes of cloud condensation nuclei, cloud droplets, and raindrops. It is relatively easy to form cloud droplets (condensation); what about precipitation? Which of the two processes below is the most important precipitation producing process in the US?

Collision coalescence process. Produces rain in warm clouds (clouds in the tropics which contain water droplets only). Falling droplets collide (why?) and stick together. Effects of cloud thickness and updraft speed on raindrop size. Which cloud type produces the largest raindrops and the heaviest precipitation? About how large can raindrops get (why don't they get any larger)?

Ice crystal process. Structure of a cold cloud. What are supercooled water droplets? Where are they found in cold clouds? Are there more water droplets or ice crystals in the mixed phase region in a cold cloud? Are ice crystal nuclei abundant or scarce in the atmosphere? Where does precipitation begin to form in a cold cloud? Why are ice crystals able to grow while supercooled water droplets do not? Riming (accretion) and graupel. Can the ice crystal process produce rain or just frozen forms of precipitation?

Types of precipitation (25 pts). Rain, virga, snow (snowflakes), drizzle, sleet (ice pellets), hail, freezing rain, graupel ("soft hail" or snow pellets). What type of cloud and special cloud characteristics are needed for hail formation?

Sample Questions       Quiz #4: 6, 9, 12, 13, 15     Final Exam: 9, 40
Tue., Apr. 7
 4 - 5 pm
 Haury(Anthropology) 129
Wed., Apr. 8
 4 - 5 pm
 Haury(Anthropology)  216