Download Chapter 18.2

Chapter 18.2
Cloud Formation
• Condensation can form dew,
fog, or clouds. Condensation is
when water vapor changes to a
liquid.
• Condensation must have
saturation to happen.
Air Compression and Expansion
• When air is compressed, the
motion of the gas particles
increases and the air
temperature increases.
• When air pressure is released
the air will expand and cool.
Adiabatic Temperature Changes
• Any temperature change that
happens when no heat is
added or taken away is called
adiabatic temperature
changes.
• This is the kind of temperature
change that happens when air
is compressed or expands.
• When air expands, it cools.
When it is compressed, it
warms.
Expansion and Cooling
• Remember as you move higher in
the atmosphere the pressure
decreases. As air moves upward
through the atmosphere it
expands and cools.
• The opposite is true for air
moving back toward Earth. It will
heat and compress.
• If air rises it will eventually cool
to its dew point. This is when
condensation takes place.
Processes that Lift Air
• Air usually resists vertical
movement.
• There are 4 ways that cause
air to rise: orographic lifting,
frontal wedging, convergence,
and localized convective
lifting.
Orographic Lifting
• Orographic lifting – when elevated
terrains (like mountains) act as
barriers to air flow.
• As the air moves up the mountain
slope clouds are made. As the clouds
move over the mountain they lose
moisture and become less likely to
give off precipitation.
• This is very important for where we
live. On the ocean side of the
mountains they will get more rain
(San Francisco area) than where we
are and even less past the Sierra’s.
Frontal Wedging
• A front is when masses of
warm air and cold air collide.
• When this happens the cooler,
denser air will act as a barrier
forcing the warmer, less dense
air to rise. This is frontal
wedging.
Convergence
• Convergence – whenever air in
the low atmosphere flows
together and lifting occurs.
Localized Convective Lifting
• On warm, summer day there may
be unequal heating of the Earth’s
surface and this causes pockets of
air to be warmed more than the
surrounding air. This warmer air
will move upward
• These warmer air parts are called
thermals.
• These are used for birds to fly
very high or people to hang glide.
Stability
• Stable air will stay in its original
position, while unstable air will
rise.
• Air stability is determined by
measuring the temperature of the
atmosphere at different heights.
• Lifting of stable air will cause
hardly any precipitation.
• Lifting of unstable air creates
thunderstorms and occasionally
tornadoes.
Condensation
• For condensation to take place, the
air must be saturated. This happens
most often when air is cooled to its
dew point.
• For condensation to take place there
usually needs to be a surface for
water vapor to condense on. Dew
forms near the ground.
• In the air there is dust, smoke, and
salt particles (these are called
condensation nuclei) and they allow
water vapor to condense on them.