MadSci Network: Earth Sciences

Re: Polar precipitation... rain on the poles.

Date: Wed Nov 16 10:08:10 2005
Posted By: In Koo Kim, Physical Atmospheric Chemistry
Area of science: Earth Sciences
ID: 1130098474.Es

The air is Antarctica is considered "dry" because all of the moisture has
already precipitated out due to the cold temperature.  In addition, cold
air simply cannot hold much water (look up the Goff-Gratch equation for water vapor partial pressures over water and ice
for more). A change in the global sea levels takes place when there is a net
displacement of water between the continents and the oceans.  

If the temperature over Antarctica rises significantly, the air may hold more
water vapor.  However, this will not lead to an overall increase in
precipitation.  The reason is because most of the moisture that feeds
precipitation over the Antarctic continent comes from the circulation of moist
air from the tropical regions.  Whereas moist air entering a "cold" Antarctica
is more-or-less immediately precipitated as snow onto the continent - moist air
entering a "warmer" Antarctica will not be precipitated as much.

In addition, an increase in temperature will cause existing ice sheets in
Antarctica to melt and break away.  Recall in 2002 when the "Larsen B" ice shelf
(about the size of Rhode Island) shattered and broke away into the ocean.  An
event like this is HUGE since it took tens of thousands of years for those ice
sheets to form.  This was a net loss of water from the continents and it
resulted in a rise in the global sea level.

- In Koo

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