Download adiabatic cloud formation - Hewlett

 ADIABATIC HEATING/COOLING
A. Adiabatic temperature changes occur when
1. Air is compressed as pressure increases
a. Motion of air molecules increases
b. Air will warm as descends due to compression
2. Air expands as pressure decreases
a. Air will cool as rises due to expansion
b. This is the most imp. process of cloud formation
B. Adiabatic rates
1. Dry adiabatic rate
a. Unsaturated air
b. Rising air expands & cools at 1◦C
/100m(10º/1000m)
c. Descending air is compressed; warms at 1◦C/100 m
Can you explain why warm air
cools as it rises?
 Imagine
a parcel of air rises after
it is warmed.
 Examine the relationship
between pressure and the
movement of air (speed and
direction).
– Adiabatic Cooling
Decrease in temperature of an expanding
gas
– Adiabatic Heating
Heating of a gas as it undergoes
compression
WINDWARD SIDE
LEEWARD SIDE
WET Air rises, expands,
cools, condensation
occurs, clouds form and
it rains.
DRY Air descends, is
compressed, and
heats up.
http://www.mrphome.net/mrp/rainsh
adow.swf
http://www.mrphome.net/mrp/rainsh
adow.swf

As a parcel of dry air is moved upward, it expands and
cools according to the dry adiabatic lapse rate. This
graph compares the temperature of a rising and
adiabatically cooling parcel of dry air with the average
temperatures of the surrounding atmosphere when the
temperature at the surface is 30OC (86O F).

When the dew point temperature is reached in a rising
parcel of air, the latent heat of vaporization is released
as water vapor condenses. This release of heat warms
the air, decreasing the density and accelerating the
ascent. The new lapse rate from the release of latent
heat is called the wet adiabatic lapse rate.
Determining Cloud
Base
What weather
variables influence
Temperature
cloud base?
Dew Point
Humidity
Air Pressure
Water Chemical Properties
Two atoms of hydrogen
One atom of oxygen
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H
H
o
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