Airplane streaks

Why do jets leave white streaks in the sky? Diane, Brinson, Georgia

Contrail, up high.  Photo courtesy of NASA.

The streaks — aptly named "contrails", which stands for "condensation trails" — are engine-made clouds. Water vapor from the turbulent jet-engine exhaust, or even from a high-flying piston-engine plane, condenses immediately as it leaves the plane and hits cold air. The trailing cloud is much like the one you make when you breathe out on a cold day and "see your breath".

Down lower, in warm moist air, the plane, plowing through the air, will drop the pressure behind its wings and propeller enough to condense water. Once again, a cloud forms, only, this time, behind the wing tips and propeller. The DC 10, in particular, makes such clouds on take off and landing.

Further Surfing:

USA Today: Evaporation and condensation

University of Wisconsin: Contrails

Jay Reynolds: A journey through the labyrinth

(Answered Jan. 31, 2003 updated on 25 July 2007)

Comments

• I just don't agree! The white streaks we see in the skies of Los Angeles are NOT Contrails. The question is what is that stuff being released into our air supply? Apparently, it isn't just occuring in my area. Governmental experiments using us as guinea pigs? Sounds more like it. The question is why? Are they trying to regulate the
  weather? Biological testing? Concerned Citizen, Elizabeth, Los Angeles, California
   
• Reply:  Interesting thought, but what makes you think they aren't contrails, Elizabeth?  Here's a link to what the government has to say:  NASA Langley Contrail Page Link.  NASA's webpage discusses studies and airs a talk show from KUSP public radio in SantaCruz, California.

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