Transcript Ch. 24.4 notes (Moisture in the Atmosphere)

Water in the Atmosphere
Objectives:
•What are some ways in which water
condenses?
•How do clouds form?
•What are major cloud types?
•What are the major forms of precipitation?
Humidity = Amount of water vapor in air
Warm tropical air contains more water than cold, polar air
•Relative Humidity =
Ratio of the amount of water vapor in the air to the
maximum amount of water vapor that can exist as that
temperature.
•Expressed as a %
•Ex.: Relative Humidity is 60%, Air contains 60% of
maximum amount of water vapor that can exist at that
temperature
•Relative humidity = 100 %, Air is SATURATED
Relative Humidity &
Dew Point
• Warmer air can hold more water
• @ night: Temps. Cool; amt. of water air
can hold decrease & relative humidity
increases.
• During day: air warms & humidity
decreases.
(even though the total amount of water in air
stays the same).
DEW POINT =
Temp. at which air is
SATURATED (RELATIVE
HUMIDITY 100%).
If temps. Drop further 
water vapor condenses
(air can’t hold any more
water)
Types of Condensation
1. Dew – water vapor
condenses on earth’s surface
(leaves).
2. Frost – dew point of air is
below freezing.
– Water doesn’t condense.
G  S (ice)
3. Fog – water vapor
condenses to form a cloud
that is near / touching ground
4. Clouds
Cloud Formation
Clouds = dense, visible mass of tiny water droplets
or ice crystals (very small) that are suspended in
the atmosphere.
Cloud formation:
1. Warm, moist air rises in atmosphere
2. Water vapor condenses when temp. drop
below dew point.
3. Condensation Nuclei – also needed
Dust, salt, solid particles needed as platforms for
water to condense on.
Cloud Type: Cumulus
• Cumulus Clouds – Puffy,
piles/heaps of cotton balls w/
flat bottoms.
• “fair weather clouds”
• Form less than 2 kms. From
ground
– Cumulonimbus = Dark towering
clouds that are ass. w/ thunder
storms. Grow vertically. (Anvil top)
“Thunder heads”
Cloud Type: Stratus
• Stratus Clouds – Flat
layers, cover much or all
of sky
– Nimbostratus = low
stratus that produce
steady, widespread rain
or snow.
– Altostratus = Middle level
clouds (2000 – 6000
meters) that produce light
rain or snow.
Cloud Type: Cirrus
Cirrus Clouds = Thin wispy feathery /veil like
clouds made up of ice crystals.
• Clear sunny days
• Don’t produce rain … but are usu. Ahead
of rain producing clouds.
• High Altitudes
Link to chart:
http://educ.queensu.ca/~science/main/concept/biol/b03/G08LABR8.gif
Forms of Precipitation
• Rain = liquid precip. Forms in nimbostrat. or
cumulonibus clouds
• Snow = ice cystals
• Hail = round, solid pieces of ice more than 5 mm
in diameter. Ice is tossed up & down in
cumulonimbus clouds and get coated w/
water that freezes  layers of ice.
• Sleet = Ice particles less than 5mm in diamter.
Rain freezes as it falls.
• Freezing Rain = rain freezes after hitting
surfaces.