Quiz
#3 Study Guide pt. 1
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Saturation. 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, condensation balances evaporation. Click here
to test yourself on this topic.
Humidity variables. See Oct. 17 notes. 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.
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.
Miscellaneous. Cooling
moist air to below its dew point and then
warming it back up. Rain shadow effect. Why are relative humidities
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 (p. 142).
Here
are a couple of relatively tough
humidity questions to answer.
Sample Questions from the Fall 2000 Quiz
Packet
Quiz #3: 3, 12, EC1, EC3 Final
Exam:
1, 49