Download Chapter 27

Evaporation, Condensation, Clouds
and Precipitation
Water
• exists as a solid, liquid, and gas
• can change from one state to another
• The change from a solid to a liquid is
called melting, liquid to a solid is called
freezing
• Heat of Fusion = +/- 334 J/g/°C
GAS
LIQUID
SOLID
Evaporation
• the process of water changing from a
liquid to a gas
• occurs when water absorbs energy from
its surroundings
• Because of this, evaporation results in the
surroundings becoming cooler (think of
sweating)
• Heat of Vaporization = 2260 J/g
EVAPORATION IS A
COOLING
PROCESS
Condensation
• the process of water changing from a gas
to a liquid
• occurs when water vapor loses energy
• Because of this, condensation results in
the surroundings getting warmer
• Heat of Vaporization = -2260 J/g
• COOL TEMPS - CONDENSATIO
• WARM TEMPERATURE EVAPORATION
CONDENSATION IS
A WARMING
PROCESS
Clouds
• formed by the condensation of water vapor
• There are three main types of clouds: cumulus,
stratus, and cirrus
– Cumulus clouds are thick, puffy clouds. They tend to
be lower in the sky
– Stratus clouds appear as low to middle sheets or
layers of clouds
– Cirrus clouds appear as high, thin or “feathery”
clouds. These clouds are made of ice crystals
• There are many forms of these types of clouds
– Ex. Cumulonimbus clouds often produce strong
thunderstorms and can form tornadoes!!
– Nimbus – rain/storm in Latin
CLOUDS have FLAT
BOTTOMS which
indicate the level of the
atmosphere where the
dew point temperature
has been reached!
• Cumulus clouds are "fair weather" clouds
and are unlikely to produce precipitation
• They form in warm air on sunny days
• Cumulus clouds can form at almost any
altitude, with bases sometimes as high as
14,000 feet
• Cumulus clouds are clouds of vertical
development and may grow upwards
dramatically under certain circumstances
• The updrafts may be caused by heating of
the air by the ground surface, the action of
a cold front, or to temperature differences
between land and ocean
• The vertical air currents results in towering
clouds with an anvil head on top called
cumulonimbus clouds
• Stratus clouds are low clouds, ranging in
height from near the earth's surface up to
6,500 feet
• Stratus clouds form flat layers or uniform
sheets
• Only a fine drizzle can form from stratus
clouds because there is no vertical
development
• Cirrus clouds are wispy in appearance, and
resemble horsetails (they are sometimes
called mares' tails)
• They are among the highest clouds, forming
at elevations of 25,000 feet and above,
where the temperatures are far below
freezing
• Cirrus clouds are formed almost entirely of
tiny ice crystals
Precipitation
• any form of water that falls from the clouds when they
become too large be supported by the air
• Forms of precipitation include:
– Rain
– Snow
– Sleet – rain that falls through air that is below freezing
– Freezing rain – rain that freezes on contact with a
surface that is below freezing
– Hail – formed in cumulonimbus clouds
(thunderstorms). These are ice balls which can be as
large as a softball!! HAIL USUALLY HAPPENS IN
THE SUMMERTIME!!
• **When water condenses on nitrate and sulfate particles
(from burning fossil fuels), acid rain is formed
Snow Level
Ice Level
Supercooled
Rain Level
Rain Level
BRRRR…I’
m
CHILL
Y!
• Precipitation does not occur the same
everywhere (OROGRAPHIC LIFT)
– Wind hits the windward side of the mountain,
rises, cools off, and condensation happens
– This forms clouds and precipitation
– As the air goes over the top, is sinks on the
leeward side
– As the air sinks, it compresses together and
gets warmed by friction
– Since the warmer air can hold more moisture,
condensation does not occur (and no
precipitation)!
• Occurs along the Sierra Nevada Mts. The
California side is wet, the Nevada side is dry