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MET 112 Global Climate Change -
Prof. Menglin Susan Jin
Department of Meteorology, San Jos State University
Clouds Formation
Clouds Climatology
Clouds and the Radiation Budget
A good repository of cloud photos in various
categories can be found
by Christina Rossetti
White sheep, white sheep,
On a blue hill,
When the wind stops
You all stand still
When the wind blows
You walk away slow.
White sheep, white sheep,
Where do you go?
A Scientist’s View of Clouds
Clouds are formed when air containing water vapor
is cooled below a critical temperature called
the dew point and the resulting moisture condenses
into droplets on microscopic dust particles
(condensation nuclei) in the atmosphere.
CLOUDS: A visible mass of liquid water droplets suspended
in the atmosphere above Earth's surface.
Video: cloud formation in Tucson
Timelapse of Tucson cloud formations
MET 112 Global Climate Change
 What role do clouds play on the Earth’s
 What would happen to our climate if clouds
were to increase/decrease?
 How does clouds formation change with
Clouds-1.mp4 –clouds and aerosols
MET 112 Global Climate Change
Clouds Roles - Importance of Clouds
 Clouds is part of hydrological cycle to move water
 Clouds is key in energy
– Clouds absorb/reflect short wave radiation
(clouds alebedo effect)
– Clouds emit longwave radiation back to space
– clouds absorb surface longwave radiation and keep
the heat in the atmosphere to warm the surface
(clouds greenhouse effect)
MET 112 Global Climate Change
100% of the incoming energy from the sun is balanced by
100% percent total energy outgoing from the earth.
incoming energy from the Sun = outgoing energy from the Earth.
since the Earth is much cooler than the Sun, its radiating energy is much weaker
(long wavelength) infrared energy. energy radiation into the atmosphere as heat,
rising from a hot road, creating shimmers on hot sunny days.
The earth-atmosphere energy balance is achieved as the energy received from the Sun
balances the energy lost by the Earth back into space.
So, the Earth maintains a stable average temperature and therefore a stable climate.
MET 112 Global Climate Change
Earth System Water Cycle
Clouds can form along warm and cold fronts, where air flows up
the side of the mountain and cools
as it rises higher into the atmosphere,
and when warm air blows over a colder surface,
such as a cool body of water.
Water in the atmosphere
 Definitions:
– Evaporation:
– Condensation:
– Precipitation:
Water in the atmosphere
 Definitions:
– Evaporation: Process where a liquid changes into a gas
– Condensation: Process where a gas changes into a liquid
– Precipitation: Any liquid or solid water that
falls from the atmosphere to the
ground. (i.e. RAIN!)
The process by which water vapor changes to a
cloud droplet
Water vapor molecules may ‘stick’ to
condensation nuclei and grow (billions) to
eventually form cloud droplet.
Examples of condensation nuclei include:
a. Dust
b. Salt
c. Smoke
 Condensation occurs primarily as temperature cools:
-colder the molecules more likely they are to ‘stick’ to
other molecules
Aerosols Affect Cloud Droplet Size
1.Aerosols serve as cloud condensation nuclie (CCN)
Ocean case
Land case
2. More aerosols, they will compete for water vapor to condense on, so smaller cloud droplet
MET 112 Global Climate Change
Zonal Mean Cloud Effective Radius
(M. D. King, S. Platnick et al. – NASA GSFC)
Why ocean has larger cloud droplets than land?
July 2006 (Collection 5)
Clouds and radiation
Cloud - Climate Interactions
Albedo effect - COOLING
 Clouds reflect incoming solar radiation.
 The cloud droplet size and total water content
determine the overall reflectivity.
Greenhouse effect - WARMING
 Clouds are good absorbers (and emitters) of long
wave (infrared) radiation.
Clouds and day to day temperatures
Imagine that you are going camping in the Sierras
with your friends. On the first day (and evening) it
is clear, while on the second day (and evening) it is
cloud. Based on this information alone:
Which day would be warmer?
Which evening would be warmer?
Explain your answers.
Which day would be warmer?
1. First day (clear)
2. Second day (cloudy)
3. Both the same
Which evening would be warmer?
1. First day (clear)
2. Second day (cloudy)
3. Both the same
Clouds types
Low and High clouds
Consider two types of clouds:
1. Low levels clouds
2. High levels clouds
Q: How is the Earth’s surface energy budget
different for low clouds compared to high
Clouds and climate
Cloud A: Low level, (dark, thick)
Excellent reflector of incoming radiation;
good absorber/emitter of infrared radiation
Cloud B: High level, light
(sub visible or thin)
Fair/poor reflector of incoming radiation;
good/excellent absorber/emitter of
infrared radiation
 So, clouds both warm and cool the earth.
 Overall, though, clouds act to cool the
Changes in clouds
 Increases in low level clouds will:
 Increases in high level clouds will:
Changes in clouds
 Increases in low level clouds will:
– cool the surface (cooling outweighs
 Increases in high level clouds will:
– warm the surface (warming outweighs
Altocumulus (possibly cirrocumulus, depending on altitude of the clouds)
Broken stratocumulus
Cumulus humilis (commonly called 'fair weather cumulus')
Clouds That Look Like Things
Explain how the earth’s climate would
change as a result of aircraft contrails.
Class Participation
Concept Map
Activity : Water Concept Map
Draw a concept map using the following terms.
You may add additional terms if you wish.
Water vapor
Liquid water
High Cloud
Low Cloud
Condensation nuclei