Lecture 5 reading assignm: A

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Lecture 5 reading assignm AK finish Ch 3, Ch
4. Hartmann 3.8, 3.9, 3.10, 3.12

• Lapse rate, change in T with height
• Atmospheric water
• quantifying water vapor in the air
• cloud formation
• fog formation
• high/middle/low clouds
• radiative effects of clouds

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Diurnal temperature cycle notice the lag
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Lapse rates and stability
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Temperature inversion when temperature increases
w. height..
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Forming a temperature inversion. Temperature
inversions trap pollution near ground, can be
important for formation of severe weather
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Atmospheric Water
Evaporationprocess by which water is converted
from liquid form to gas
It takes energy!
It occurs more easily over warmer surfaces.
Evaporation is also greater when atmospheric
pressure is low, wind speed is high and there
is little water vapor in the air.
Equilibrium when air is saturated
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Measuring water vapor in the air

• Mixing ratio (units g/kg w.r.t. dry air)
• Vapor pressure (at most 40 mb)
• Saturation vapor pressure
• Relative humidity
• Vapor pressure/saturation vapor press x 100
• Dew point temp to which cool air at same
  pressure to cause condensation
• Frost point temp to which cool air at same
  pressure to cause frost to form

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The source of water vapor is at the surface.
Thats why it decreases sharply away from
surface.
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Condensation/deposition Cloud formation, i.e.,
forming liquid droplets and solid ice crystals
from water vapor
Solute effect
Curvature effect
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Cloud formation

• Nucleation (formation of cloud droplet around any
  type of particle.)
• Homogeneous nucleation
• Heterogeneous nucleation
• Condensation nuclei
• Hygroscopic nuclei
• Hydrophobic nuclei
• Ice nuclei

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Fog types and formation

• Radiation fog. Forms similar to dew
• Ground cools by radiation on long clear nights
  with light winds
• Advection fog
• When warm air advected over a cool surface
• Off the coast of CA, cool coastal current
• Gulf of Mexico in fall winter
• Evaporation (frontal or steam) fog
• When water evaporates from rain that falls from
  warmer air into cold air near surface
• Upslope fog

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Fog can at most form drizzle. Traffic hazard
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Lifting mechanisms forming clouds
LCL
updraft
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Cloud classification

• Layered clouds -- stratus (layered)
• Convective clouds --- cumulo (heap)
• Clouds are also classified by their altitude
• Cirro (high composed of wispy ice crystals)
• Alto (in mid-troposphere)
• Nimbus (rain)

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Cloud classification
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Stratus is a very common cloud type in S Cal
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Cumulus Fair weather Cu
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Nimbostratus (Ns) are deep layered clouds that
bring precipitation and appear dark gray
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Cumulonimbus (Cb)
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Altocumulus (Ac)
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Radiative effects of clouds

• Clouds reflect solar radiation effectively
• Thicker clouds reflect more cooling effect
• Clouds absorb emit terrestrial radiation
• The altitude of a cloud is important in
  determining radiative budget
• Because the higher the cloud, the colder it is,
  and the less OLR it emits to space
• Clouds can cool or warm the planet

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Globally and annually averagedradiative effects
of clouds

• If clouds were removed without any other change
  then the Earth would gain approximately 20 W/m2
  in net radiation and consequently it would warm.

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Cloud composition water clouds/ ice crystal
clouds
Whether clouds originate over land or ocean
affects the number of CCNs
Shape of crystal depends on the environmental
temperature