"Joe" wrote in message
...
The chicken or the egg?

Which came first? The low pressure or the storm?

In simple terms, help a dummy understand if the low pressure causes the
storm,
or is the low pressure a byproduct of the storm?

And why in the hell does the pressure rise and fall?

Thanks,
Joe


OK, I'm thinking I'm back in front of my 8th. grade Earth Science class
and a student has asked a question, actually several questions. Let's take
the second one first. When we refer to air pressure, we are referring to a
measure of the pressure/weight pushing down on the earth's surface of a
column of air extending from the surface of the earth to the top of the
atmosphere. On average the weight of a 1" square column of air is 14.7 lbs.
If that air is heated by the sun, it will become less dense and begin to
rise. Hence the weight of that rising column of air pushing down on the
earth's surface is less than it was before, producing a lower pressure. On
the other hand, if that column of air were to lose some heat energy, that is
cool down, it would become more dense/heavier and exert a higher pressure.

The second question is a little more difficult, but here goes. I would
suggest that the lower pressure precedes a storm at least in an observable
sense. When air is heated by the sun, it will expand and become less dense,
and rise. This will cause a lowering of the air pressure. Remember, air
pressure is a measure of the weight of air on the surface of the earth. Air
will begin to flow in from surrounding areas to replace the air that is
rising. A number of factors including the Coreolis Effect will eventually
cause the "low pressure area" to begin to develop a counter-clockwise motion
in the northern hemisphere.. This motion is similar to water flow down a
drain. At some point the characteristics of a "storm" will develop; clouds
and eventually precipitation. Hope this helps a bit.

Neil