Download 14-HumidityAndClouds

Humidity and
Clouds
WATER is the most
important GAS for
understanding weather!
Moisture: Change of State
ChangesHeat
of state
absorbedof Water
Heat released
What happens to molecules
and heat during a change of
state?
• Heat absorbed = molecules move apart
(density decreases)
• Heat released = molecules move closer
(density increases)
What are humidity and
saturation?
• Humidity = amount of water vapor in
air
• Saturation = when air holds the most
water vapor possible
– depends on temperature and pressure
How do warm and cold air
compare?
• Warm air holds MORE water than cold
air!
– This helps explain why you feel the
humidity more on a hot day
Warm air holds more moisture than cold
air.
What is relative humidity?
• Relative Humidity (RH) = ratio of the
amount of water in the air versus the
amount of water air can hold when
saturated
– Changes with temperature/pressure
• RH
= actual content
potential
X 100
What is Dew Point?
• Dew point = the temperature at
which water vapor turns to liquid
– High dew points means moist air
– Low dew points mean dry air
Dew on a spider web
What is a cloud?
• A group of tiny water drops or ice formed around
a bit of dust or salt
• Clouds form when the dew point is reached!
4 ways that clouds form
Convection
• How do clouds form from convection?
• Warm moist air flows upward in convection
currents to form clouds
Orographic lifting
Explain…
Orographic lifting
• Mountains act as barriers to the flow of air,
forcing the air to move upward, forming a
cloud
Frontal lifting/wedging
Explain…
Frontal lifting/wedging
• What is a front?
– a boundary or edge where two air masses meet
• Warmer, less dense air rises above the cooler air,
causing clouds, condensation, and storms
Convergence
Explain…
Convergence
• Air masses with the same temperatures
crash into each other and both rise
Temperature Inversion
• When air found at lower levels is actually
cooler than the air above it
– it is more dense so it stays below
This can happen on a cool night - land cools quickly, causing the air
above it to cool as well
Temperature inversions can create smog in cities with high pollution
(polluted air stays low and blankets city)
Clouds are classified by….
•Shape
•Height
Shapes of Clouds
•
•
•
•
Stratus…
Cumulus…
Cirrus…
Nimbus…
Describe each type!
Heights of Clouds
• Height is determined by
where the base of the
cloud is
– High (cirro-)
– Middle (alto-)
– Low (strato-)
• Cloud names come from
combining the shape and
height descriptions…
– e.g., cirrostratus, altocumulous
Base
High clouds = ice crystals
Cirrus Clouds
Cirrostratus
Cirrocumulus
Middle clouds = ice crystals & water droplets
Altocumulus
Altostratus
Low clouds = water droplets
Cumulus
Stratus
Stratocumulus
Nimbostratus
Cumulonimbus Clouds
(thunder clouds)
• Very tall clouds, extending to the
tropopause (top often shaped like an
anvil)
• Intense weather:
– lightning & thunder
– hail
– tornadoes
– heavy rain
Fog
• Fog is a cloud with its base on the
ground
Your summary box…
• Take a few minutes to summarize your notes
on humidity and cloud formation
• You may discuss with your table partner