Clouds
First midterm exam is soon!
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exam will be in-class, during our regular lecture on Thursday
February 7 at 3:00 pm
• Review for the exam will be held on Tuesday in class.
• Practice tests are available at the class web page “Exams”
• The exam will be CLOSED BOOK
♦ No textbooks
♦ No calculators
♦ No cheat-sheets
Alternate seating
Bring a picture ID
The grades will be posted on e-Learning.
The exam covers Chapters 1,2,3,4,5.
For a list of sections which are not covered, see the Class Notes
on the class web page:
www.phys.ufl.edu/~katia/Teaching/MET1010/ClassNotes.htm
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RECAP
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• Haze - condensation on small airborne particles.
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Dew - condensation on cold surfaces.
Frost - deposition on very cold surfaces.
Fog – saturated wet haze, visibility <1 km.
♦ Radiation fog – driven by radiation cooling
♦ Advection fog – driven by air movement
♦ Upslope fog - topography driven
♦ Evaporation fog – cold air above warm body of
water.
Clouds
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• Classification: four major cloud groups according to the
Definition: visible aggregate of tiny water droplets or
ice crystals suspended in air
height (of the cloud base). Within each group there are
different types identified by their appearance
♦ High (cirrus: Latin for “wisp of hair”)
Cirrus, Cirrostratus, Cirrocumulus
♦ Middle (alto, from the Latin altus: “high”)
Altostratus, Altocumulus
♦ Low (stratus, Latin for “layer”)
Stratus, Stratocumulus, Nimbostratus
♦ Clouds with vertical extension (cumulus: ”heap”)
Cumulus, Cumulonimbus
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What are the important things to know
• temperature drops with altitude.
Composition: recall that in the troposphere the
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♦ High clouds (16,000 – 43,000 ft in midlatitudes)
are made mostly of ice
♦ Middle clouds (6,500 – 23,000 ft in midlatitudes)
are composed of water droplets and some ice
crystals (higher up or when the temperature is low)
♦ Low clouds (surface to 6,500 ft in midlatitudes)
are composed primarily of water droplets except in
very cold weather when it snows
For reference: commercial aircraft flies around
30,000 ft.
Basic Cloud Types
High Clouds
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• Composed mostly from ice crystals.
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Form at high altitudes (above 16,000-20,000 ft).
Appear white and very thin.
Cirrus clouds (this transparency’s background):
♦ thin wispy clouds
♦ blown by strong high altitude winds (jetstream)
♦ typically move from west to east (?)
♦ point to fair, pleasant weather
???cumulus types
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• Cirrocumulus (high)
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Small, rounded puffy, in
parallel waves or bands
♦ “mackerel sky”
Altocumulus (middle)
Stratocumulus (low)
???stratus types
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♦ Halo around sun/moon
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Cirrostratus (high)
Altostratus (middle)
♦ Sun dimly visible
Stratus (low)
♦ No sun, like thick fog
Cumulonimbus cloud
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• Large vertical extent (several km thick).
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• All types of precipitation is possible: strong
Thunderstorm cloud with a very dark base.
The top may be flattened by winds (anvil).
It can occur as a single isolated cloud or a wall of
clouds.
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showers, snow, hail. Lightning is very likely.
Tornadoes are possible.
They are associated with large amount of energy
release, strong up- and down-drafts.
Other types of clouds
• Clouds driven by topography:
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some sort of a barrier present:
♦ Cap clouds: wind over a mountain or
♦ Lenticular clouds: formed over a mountain
♦ Banner cloud: downwind of an isolated mountain top.
Mammatus clouds: typically under cumulus clouds.
Condensation trails from jet aircrafts: adding water vapor,
providing condensation nuclei, cooling of the air flowing over
the wing.
Very high altitude clouds:
♦ noctilucent clouds: 75-90 km above the surface;
♦ Where is the water coming from? - meteorites, CH4
chemistry.
Cap cloud
Lenticular clouds
The clouds form on the lee side of the
mountains in the crests of the mountain
wave.
Can be confused with UFOs
Banner cloud
Observing the Earth from Space
• Geostationary satellites:
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♦ Orbit the equator at the same rate
as the Earth spins at about 36000
km above the surface.
♦ Remain above a fixed spot on the
Earth surface.
♦ Provide continuous monitoring of a
specific region
Polar-orbiting satellites.
♦ Provide global coverage of the
planet, move slightly westward on
each pass
♦ Have a lower orbit (~850 km).
♦ Observe the area straight beneath
them.
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Satellite observations
Visible wavelengths:
♦ Use the reflected sun light from the top of the
clouds.
♦ The albedo of the clouds gives information about
the thickness of the cloud.
♦ No temperature information about the clouds.
Infrared observations:
♦ IR light emitted from the clouds.
♦ Provide T information about the clouds.
♦ This can be converted into altitude information.
♦ Using different wavelengths in the IR one can
obtain 3D information about the structure of the
clouds.
Name that cloud!
Cirrocumulus
Altocumulus
Altostratus
Cirrostratus