Anyone who has ever seen a streaky line of vapor, known as a contrail, behind a high-flying aircraft knows that airplanes can produce their own clouds. But in rarer cases, aircraft can also punch round holes, such as the one over Antarctica pictured here, or carve long channels through existing, natural clouds. Those formations arise from the strong cooling effects of airflow over a plane’s propeller blades or a jetliner’s wing. A study published recently in the journal Science reports that cooling can spontaneously freeze water droplets in the cloud and stimulate precipitation. The phenomenon requires a specific set of cloud conditions and is thus unlikely to have significant large-scale effects, but it could affect regional weather near airports. 

3 Comments

1. 1. promytius 01:36 PM 9/3/11

   WOW! You may have just solved a twenty year old mystery! In the deep of winter, we were flying back to Massachusetts from Florida. It was late in the day; looking out the window, we saw a distinct black, long and straight shadow on the ground, parallel to the flight path. It persisted for maybe 15 minutes, coming and going, but always straight, and always parallel, and was observed by many, but no one had a clue as to what it was. Maybe it was the jet slicing the clouds, and they cast a shadow from the edges. I will at least consider this case closed!
   

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2. 2. R.Blakely 01:11 AM 9/10/11

   In air, water vapor is like helium since water has a molecular mass about half that of air molecules. Clouds form as moisture rises and concentrates. Clouds float in air because they have more water vapor than surrounding air, and so they act like blimps. Clouds help to regulate temperature by reacting to oppose change. For example, cooler weather causes fewer clouds, which reflect less sunlight.
   Airplane contrails form from vapor, which condenses and then immediately cools since droplets emit more infrared than vapor molecules. Water vapor tends to become super cooled since water vapor molecules rise continuously in air. The rise ends when the formation of droplets begins, and greater mass of the droplets balances the lower mass of the rising vapor.

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3. 3. Quinn the Eskimo 01:11 AM 9/10/11

   Okay, quiet down now. Recess is over. Time to string some beads. Children, walk like adults and quietly into the classroom. SIT DOWN.
   
   -- Mrs. Okin, 1st Grade Teacher. Some lessons stick.
   
   
   

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