Pressure, Altitude and Weather Systems
The standard atmospheric pressure at sea level is
29.921" Hg. at 25,000 feet, 11.10" Hg, 50,000 feet, 3.436" Hg. Now
on a rainy day, at sea level, it may be, say 29.0". Is it still the
same differences at 25,000 feet and 50,000 feet? Perhaps 25,000 ft
will change, and 50,000 ft will not change since it is above the
rain bearing clouds? In other words, is a low pressure system
effecting pressure at all altitudes?
This is a great question.
The standard atmosphere values are an average and rarely
occur at a particular location. Whenever there is an
atmospheric system in the vicinity, whether a high pressure
or a low pressure system, the pressures at various altitudes
can be affected by that system.
In the case of your low suggested low pressure system, the
pressure at a particular altitude is affected by the strength
and depth of the low pressure system. Very strong low pressure
systems (which, by the way, have the lowest pressures) often extend
very high up into the atmosphere and thus lower the pressure
at a large range of altitudes. Weak low pressure systems have less
affect on pressure with altitude.
You can tell the strength of a low pressure system by looking at
the weather (or pressure) maps at the surface, 850 mb, 500 mb, and
300 mb. If you see a closed low or a deep trough all the way up
through 300 mb (particularly if the center of the low at those
levels is in the same location), you can assume that it is a strong
and active low pressure system.
The presence of clouds and precipitation does not always reflect
an affect on pressure with altitude. But it is likely that if it is
raining as a result of a low pressure area being present, the
pressures at most altitudes will be lower than the standard
David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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Update: June 2012