Principle
The
changes in the atmosphere with height are results of specific
physical conditions which exist on the earth and in its atmosphere.
The vertical changes in temperature are important in constraining
weather events to the lowest 10-12 km of the atmosphere. The ozone
layer, located near 25 km above the earth's surface, causes
the temperature to rapidly change in the middle atmosphere. |
Figure 2 -
Relationship Between Pressure and Height in the Atmosphere
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Changes
in Air Pressure with Height
- Pressure always decreases with height and does so most
rapidly near the ground. Why do sealed balloons increase
in volume when they rise in the atmosphere? Why do your
ears "pop" when you ride on an elevator in
a tall building or when you take off in an airplane?
As we move upward in the atmosphere, the
weight of the air upon us should decrease because there is
less air above us. Thus, air pressure decreases with increasing
height.
- Pressure decreases with height more rapidly near the
ground because the atmosphere is a gas which can compress
in its response to the earth's gravitation effect.
- If more air is packed into the same length vertical
column, then the air column will weigh more and, hence,
the air pressure will be greater.
So we may have horizontal
variations of pressure if two air columns are next
to one another, both of the same height but one
with more molecules packed into it than the other.
This is how we get high and low pressure systems.
- The rate at which air pressure changes with height
is determined primarily by the average temperature in
the column under consideration.
In colder regions, atmospheric
pressure decreases more rapidly with height than
normal or than is observed in warmer areas.
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Changes in
Air Temperature with Height
- Temperature has a more complicated structure, mostly
because the temperature of the air relies on the energy
its molecules receive from radiation.
The two main sources of radiation in the
atmosphere are the sun and the earth. The sun's radiation is
mostly near infrared (37%),
visible (44%), and ultraviolet (7%) while the earth's radiation
is mostly far infrared. Infrared is generally what we feel
as "heat", visible is what we see, and ultraviolet is
what our skin absorbs to make us tan or burn. The temperature
structure of the atmosphere is controlled significantly by
whichever of these three types of radiation are affecting the
region.
- Temperature generally decreases with height in the
lowest 10 km or so above the earth's surface.
This 'layer' is called the
troposphere. How can we tell temperature decreases
with height? Do mountains give us a clue?
- Temperature increases with height from about 10 km
to 50 km above the earth's surface.
This
layer is called the stratosphere and results from absorption
of solar radiation by ozone. How can we "see" the
change from the troposphere to the stratosphere? The
tops of large thunderstorm clouds can show us.
- Temperature again decreases and increases with height
above the stratosphere.
These layers are called the
mesosphere and thermosphere, respectively.
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