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Available Moisture as Rain
Name: Art
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
What percent of available moisture in the atmosphere falls as rain?
Replies:
Art,
Only about 0.001 percent of Earth's water is in the atmosphere,
and perhaps only a few percent of that is really available at any
one time to be used for precipitation. Most of the water vapor
in the atmosphere gets cycled through precipitation every few weeks,
although some in the upper parts of the atmosphere may remain there
for months.
David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory
That is very difficult to say because the "available" moisture, by which
I assume the amount of water vapor present, is difficult to determine. It
depends upon the temperature of the air, which in turn depends upon
altitude, the movement of the air (e.g. up and over mountains), supersaturation
of the atmosphere(i.e. clouds, fog, snow, etc.), relative humidity -- the list
is long and overlapping. There are many of these variables that need to be
specified in order to give a credible answer.
Vince Calder
Art,
Virtually all of the water in the atmosphere ends up
being precipitated, although it could take a very
long time before water in the stratosphere, for instance,
would be precipitated out. The 5% figure that you quote
sounds like the amount that is available at any one time
(I said "a few percent") for precipitation.
Since most of the water vapor in the atmosphere is in the
troposphere, where the active weather systems are, almost
all of it gets cycled (precipitated) within several weeks,
with the average residence time of a water molecule in the
atmosphere being only about 10 days.
David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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Update: June 2012
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