Download Ch. 24.4 Water in the Atmosphere

Ch. 24.4 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
• As temps. decrease (at night), amt. of
water air can hold decrease and relative
humidity increases. During day, temps.
increase and relative hum. 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)
Water condenses at Dew Point
(temperature)
• Dew – water vapor
condenses on earth’s
surface.
• Frost – dew point of air is
below freezing.
– Water doesn’t condense.
G  S (ice)
• Fog – water vapor
condenses to form a cloud
that is near / touching
ground
• 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.