This is news? …
Originally posted by The Hindu:
Through a ‘seeding' process, the aircraft leave behind odd-shaped holes or channels in the clouds that have long fascinated the public.
As turboprop and jet aircraft climb or descend under certain atmospheric conditions, they can inadvertently ‘seed' mid-level clouds, causing narrow bands of snow or rain to develop and fall to the ground, new research finds.
The key ingredient for developing these holes in the clouds: water droplets at subfreezing temperatures, below about -15 degrees Celsius.
As air is cooled behind aircraft propellers or over jet wings, the water droplets freeze and drop toward Earth.
“Anytime aircraft fly through these specific conditions, they are altering the clouds in a way that can result in enhanced precipitation nearby,” says Andrew Heymsfield.
Dr. Heymsfield is a scientist with the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, and lead author of a paper reporting results of research into the phenomenon.
A similar process can occur with jet aircraft, which need colder temperatures (below about -20 to -25 degrees C) to generate the seeding effect.
Air is forced to expand over the wings as the aircraft moves forward, cools, and freezes the cloud droplets, according to a National Science Foundation (NSF) press release.
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What happens is that as air rises, dirt sediments out and the upper atmosphere tends to be cleaner than stuff near ther surface. Dirt gets into the air from smoke, dust-storms and agricultural and forest pollen. It's all quite natural.
When air rises it cools at a regular pace called the Adiabatic Lapse Rate.
It is held in a system called a Low. The air is a fluid in a reservoir -as near as damn it.
And the heat exchange processis virtually contained in the system.
When the clean air raches the tropopause it may leave the train and become part of a larger reservoir full of very clean air. Then the spell changes and the acoustic wave is holding a huge supply of wet air that is supercool.
When nature takes its course, this layer will condense its water as ice. If it forms slowly enough, it will form snow. But a rapid transfer will allow seeds to form and then the stuff will drop.
As it drops it can pick up more water, becoming large hail or rain and it can sublimate. It can return to the air or even rise back in a rotaing stream. All sorts of things are possible.
And all this research has uncovered is that aircraft can influence things.
If you observe enough condensation trails (con-trails) you will notice this condensate forming occasionally. But you will only see it on clear days. And clear days are the days when the situation is most likely to be just right for it to happen. On cloudy days, the phenomenon has already occurred.