Cloud Types and Precipitation

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Transcript Cloud Types and Precipitation

Warm Up 3/18/08
The wet adiabatic rate of cooling is less than the dry
rate because ____.
a. of the dew point
b. of the release of latent heat
c. wet air is unsaturated
d. dry air is less dense
2) Cool air acts as a barrier over which warmer, less
dense air rises, in a process known as ____.
a. divergence
c. orographic lifting
b. frontal wedging
d. subduction
3) Orographic lifting is associated with ____.
a. mountains
c. fronts
b. flat plains
d. rivers
Answers: 1) b. 2) b. 3) a.
Cloud Types and Precipitation
Chapter 18, Section 3
Types of Clouds
Clouds are classified on the basis of their
form and height
Cirrus clouds are high, white, and thin
Cumulus clouds consist of rounded
individual cloud masses, they normally
have a flat base and the appearance of
rising domes or towers
Stratus clouds are sheets or layers that
cover much or all of the sky
There are three levels of cloud heights:
high, middle, and low
Three cloud types make up the family of high clouds
(above 6000 meters): cirrus, cirrostratus, and
All high clouds are thin and white and are often made
up of ice crystals
Clouds that appear in the middle range (~2000-6000
m) have the prefix altoMiddle clouds may cause infrequent light snow and
There are three members in the family of low clouds
(below 2000 m): stratus, stratocumulus, and
Nimbostratus clouds are the main precipitation makers
Vertical development clouds have their bases in the
low height range, but extend through the middle or
high altitudes
Cumulonimbus may produce rain showers or
Classification of Clouds
Concept Check
What does the Latin word stratus mean?
Stratus means “to cover with a layer”.
Fog is defined as a cloud with its base at or very
near the ground
A blanket of fog is produced in some West Coast
locations when warm, moist air from the Pacific
Ocean moves over the cold California Current
and then is carried onshore by prevailing winds
Fogs also can form on cool, clear, calm nights
when Earth’s surface cools rapidly by radiation
When cool air moves over warm water, enough
moisture may evaporate from the water surface
to produce saturation; as the rising water vapor
meets the cold air, it immediately condenses and
rises with the air that is being warmed from
Distribution of Fog
Concept Check
Compare and contrast clouds and fogs.
Clouds and fogs are physically the same.
Fogs are clouds with their bases at or very
near the ground.
How Precipitation Forms
For precipitation to form, cloud droplets must grow in volume
by roughly one million times
Bergeron Process – a theory that relates to the formation of
precipitation to supercooled clouds, freezing nuclei, and the
different saturation levels of ice and liquid water
Supercooled – water in the liquid state below 0ºC (in the
atmosphere pure water can reach -40ºC without freezing)
Supersaturated – the condition of air that is more highly
concentrated than is normally possible under given temperature
and pressure conditions
Because the level of supersaturation with respect to ice can be
quite high, the growth of ice crystals is rapid enough to
produce crystals that are large enough to fall
Collision-Coalescence Process – a theory of raindrop
formation in warm clouds (above 0ºC) in which large cloud
droplets collide and join together with smaller droplets to form
a raindrop
Collision-Coalescence Process
Concept Check
What must happen in order for
precipitation to form?
Cloud droplets must increase in volume by
about one million times.
Forms of Precipitation
The type of precipitation that reaches Earth’s
surface depends on the temperature profile in
the lowest few kilometers of the atmosphere
Temperature profile is the way the air changes
with altitude
Rain means drops of water that fall from a cloud
and have a diameter of at least 0.5 mm
At very low temperatures light, fluffy snow made
up of six-sided ice crystals forms
Sleet, glaze, and hail are all formed from water
becoming supercooled on its trip down to the
Read Chapter 18 (pg. 504 – 522)
Do Chapter 18 Assessment #1-30 (pg. 527528)
Study for Chapter 18 Quiz!