Quiz
#3 Study Guide
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Greenhouse
effect
(simplified
view)
(15 - 20 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
(5
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 wo questions are a little harder: (i) How is it possible for the
earth's surface to emit
more radiant energy than it gets from the sun? (ii) On average
does the earth's surface get more radiant
energy from
the
sun or from the atmosphere? Humidity variables (30 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 vaor 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 ()
- 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
(15 pts).
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. Sample Questions
from the Fall
2000
Quiz
Packet
Quiz #3: 3, 12, EC1, EC3 Final
Exam:
1, 49
Dew,
frozen dew, frost (10 pts).
How do these differ (Is the nighttime minimum temperature, Tmin, above
or below freezing; is the dew point temperature, Td, above or below
freezing; is Tmin warmer or colder than Td)?
Cloud
condensation nuclei (CCN)
(10 pts).
Do CCN make it harder or easier for clouds to form? Typical
concentrations. Hygroscopic nuclei.
Dry haze, wet haze, and fog. "Cloud in a bottle" demonstration.
Clouds clean the atmosphere.
Cloud
identification
and
classification
(30
-
40 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 (handrawn) 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.
Sample Questions
Quiz
#3:
9,17
Quiz
#4:
1,4,10,EC2
Final Exam: 8,44,50
Satellite
Photographs
(0 pts). Infrared and
visible photographs. What do white and
grey on these two types of photographs represent? Thunderstorms
can produce severe weather; how would a thunderstorm appear on VIS and
IR photographs? How can satellites view clouds at night?
How is it possible to see air motions in regions where there aren't any
clouds? Geostationary and low-earth orbit satellites. Here
is a sample satellite photograph question.
Sample
QuestionsQuiz
#4: 16 Final Exam: 38
Formation
of
precipitation
(20 - 30 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). Graupel. Can the ice crystal
process produce rain or just frozen forms of precipitation?
Types of
precipitation (15 - 20 pts).
Rain, virga, snow (snowflakes), drizzle,
fall streaks, 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?