Atmospheric Lifting Notes File

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Lifting and Cooling
Four major processes
make clouds form
Adiabatic Cooling
Mixing
Lifting
Advective Cooling
Warm air can hold
more moisture than
cold air
Adiabatic COOLING
a change in
temperature due
solely to a change in
altitude


dry adiabatic lapse
rate= 10c/km
Moist adiabatic lapse
rate= 6C/km
The reason for the
difference is that latent
heat is released when
water condenses
water's high heat of
vaporization creates a
significant release of
the energy when it
condenses (and is an
important source of
energy in the
development of
thunderstorms)
Atmospheric Lifting
For clouds to form air must lift
3 lifting mechanisms



Convectional
Orographic
Frontal
Convectional Lifting
Some areas of
Earth's surface pick
up heat better than
others.
As air warms it
becomes less dense
and rises. As it rises
it cools and sinks
Circulatory motion is called
convectional lifting
If cooling occurs
close to the air's
saturation
temperature,
condensing
moisture forms a
cumulus cloud
Form and dissipate
over the same area
Orographic Lifting
An air mass lifts
when it is pushed
upward over an
obstacle such as a
mountain range
As rising air cools, if it is
humid, it forms a cloud.
If stable air stratus
If unstable air
cumulus
As air moves down the other slope it warms
The descending air is dry because the
moisture was removed on the other side
This is called the
Rain Shadow Effect.
Example: Eastern
Colorado and
western Kansas
See figure 27.10
Frontal Lifting
When fronts collide warm less
dense air is forced up over cold
dense air
Fronts—dryline
The source region for cT air is the desert Southwest, the high
plains and Mexico with relation to the United States. The air has
low dewpoints and warm to hot afternoon temperatures but with
mild nighttime temperature. Skies are generally clear in cT air.
This allows daytime heating during the day and radiational cooling
at night. The cT air mass is most prevalent in summer; in the cool
season it is not as discernible. Due to the buoyancy and elevation
of cT air across North America, this air will advect into the midlevels of the atmosphere once it moves out of its source region.
This creates a cap of mild dry air. If this air advects over PBL mT
air, the severe thunderstorm threat increases significantly. The
boundary of cT is most noticeable with the creation of a dryline. A
dryline separates mT air from cT air. Depending on the strength of
the dryline, convergence along the dryline and the dynamics
above the dryline, severe thunderstorms can form near a dryline
boundary.
Advective Cooling
The process by which the temperature
of an air mass decreases as the air
mass moves over a cold surface


Cold ocean
Land surface
Precipitation
Any moisture that falls from the air to
Earth’s surface
Four major types




Rain
Snow
Sleet
Hail
Rain
Classified by droplet
diameter
Fine mist to large
droplets
Measured with a rain gauge
Here is a tipping
bucket rain gauge
Sleet
Ice pellets
Or ice glaze


Does not freeze till it
hits a cold surface
This is commonly
called an ice storm
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