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Chapter 18 Review
Place these notes into your
Meteorology Notebook
The number of grams of water vapor in the air is
called the specific humidity.
Example:
16 g/kg
A comparison of the actual amount of water
vapor in the air with the maximum amount
of water vapor that can be present in the
air at a given temperature and pressure is
called relative humidity.
The specific humidity of air is 16 grams per
kilogram, and the capacity of the air is 80
grams per kilogram, the relative humidity
is 20%. Or: The specific humidity of air is
24 g/kg, and the capacity of the air is 80
g/kg, the relative humidity is 30%.
Specific humidity of air in g/kg
------------------------------------------------=
Capacity of air in g/kg
24 g/kg
----------------80 g/kg
0r
16 g/kg
----------------80 g/kg
= Relative humidity @ 30%
= Relative humidity @ 20%
Relative humidity
Condensation of water vapor in the air occurs
when the temperature drops below the point
at which the air’s capacity to hold water and
specific humidity are the same. (dew point)
Fog droplets remain suspended in air because
they are supported by slight movements of
air. ad “toward” and vection “to bring”
Advection fog:
Particles that do not usually act as
condensation nuclei are ozone
particles.
Dust, smoke, salt, sulfur, nitrate particles
all act as condensation nuclei.
The temperature at which condensation
begins is called the dew point.
If both wet-bulb and dry-bulb thermometers
read the same, the air is considered to be
saturated.
The moist-adiabatic lapse rate is much slower
than the dry-adiabatic lapse rate.
Dry: unsaturated air cools at 10ºC/kilometer
Moist: saturated air cools varying from 5ºC/km
to 9ºC/km. p.399
As air rises, the approximate rate of cooling if
no water condenses is 10ºC/kilometer.
In a cumulonimbus cloud, heat from
condensation keeps the rising air inside
the cloud warmer and less dense than
the air around it.
When the temperature of a cloud is below
-20ºC, the cloud consists almost entirely
of snow and ice crystals.
A stratus cloud forms in stable air.
Clouds can form in any altitude in the
troposphere.
If a cumulus cloud does not have a continuous
supply of moist, warm air, it may evaporate.
(Watch this example)
Meteorologists predict the condensation level
and how tall clouds will grow by considering
the air temperature at different elevations,
the dew point, and the cooling rate of rising
air.
Fog is not considered to be a major form of
precipitation.
Advection fog will form when warm, moist
winds blow over snow covered ground.
(Watch this animation)
Clouds will contain water droplets of
various sizes. Some large; some small.
The dark gray layers of clouds that
produce a steady rain are nimbostratus
clouds.
Windward vs. Leeward
Air Movement
Condensation Level
• Artificial rainmakers where invented and
used during WWII to created inclement
weather so enemy aircraft could not see
their targets (In Theory). Silver iodide
was used as condensation nuclei in this
process.
Essay #1
What types of clouds will form when a body of
warm, moist air rises to a region of dry, stable
air? Explain why and how they form.
Cumulus clouds will form.
Cumulus clouds grow vertically.
Warm air rises and cools, causing condensation.
Clouds grow upward until temperature and density
of inside of cloud is same as outside air.
Essay #2
Explain how ice crystals grow in a cloud. Under what
conditions will ice crystals fall as snow? Under what
conditions will the ice crystals form hail?
Upper layers of clouds contain ice crystals and
super-cooled droplets. As super-cooled droplets
evaporate, the water vapor is deposited on ice
crystals. Heavy crystals fall, clumping together to
form snow.
If the snow doesn’t fall through a layer of warm air
that melts it into rain, it may reach the ground as
snow .
Hail forms when a growing ice crystal is kept aloft by
updrafts and continues to grow into a large ice
clump. Bonus points: As the hail is carried up it then
refreezes adding to its diameter. Bonus: Show a
drawing depicting this concept.
http://www.classzone.com/books/earth_scienc
e/terc/content/visualizations/es1805/es1805
page01.cfm
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