Quiz #3 Study Guide Pt. 1
Humidity variables (45 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 to
review this material on humidity variables. Here is a
reasonably challenging
humidity variable question.
Miscellaneous
(30 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 There were also several
Optional Assignments covering this material