Download Introduction - Department of Meteorology and Climate Science

MET 112 Global Climate Change -
CLOUDS and CLIMATE
Prof. Menglin Susan Jin
Department of Meteorology, San Jos State University
Outline
Clouds Formation
Clouds Climatology
Clouds and the Radiation Budget
Clouds
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.
http://earthobservatory.nasa.gov/Library/glossary.php3
A good repository of cloud photos in various
categories can be found
at www.cloudappreciationsociety.org/gallery
Video: cloud formation in Tucson
 http://www.youtube.com/watch?v=NiCSk1zxME
s
Timelapse of Tucson cloud formations
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MET 112 Global Climate Change
Questions
 What role do clouds play on the Earth’s
climate?
 What would happen to our climate if clouds
were to increase/decrease?
 How does clouds formation change with
pollution?
Video
 http://www.met.sjsu.edu/metr112videos/MET%20112%20Video%20Librarywmv/clouds/DTS-5.wmv
DTS-5.mp4
Clouds-1.mp4 –clouds and aerosols
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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)
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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.
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http://www.srh.noaa.gov/jetstream//atmos/energy.htm
MET 112 Global Climate Change
Earth System Water Cycle
Clouds Formation
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.
http://earthobservatory.nasa.gov/Library/glossary.php3
Water freely
evaporating and
condensing
Since more water
molecules are
evaporating than
condensing, then net
evaporation is
occurring.
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MET 112 Global Climate Change
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!)
Condensation

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
CCN
Land case
CCN
2. More aerosols, they will compete for water vapor to condense on, so smaller cloud droplet
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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)
Aqua
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?
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
earth
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
warming)
 Increases in high level clouds will:
– warm the surface (warming outweighs
cooling)
Cirrus
Altocumulus (possibly cirrocumulus, depending on altitude of the clouds)
Stratocumulus
Broken stratocumulus
Nimbostratus
Cumulus humilis (commonly called 'fair weather cumulus')
Cumulus
Cumulus
Cumulus
Cumulus
Cumulonimbus
Stratus
Stratus
Cirrus
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
Ice
Liquid water
Condensation
Evaporation
Gas
High Cloud
Low Cloud
Precipitation
Condensation nuclei
Temperature
Warming
Cooling
Air