Contrails: Why they linger longer more on some days than others

Questions prompt explanation of contrails

INDIANAPOLIS - Dozens of leftover contrails were visible above Indianapolis on Monday morning, leading some to question why they were there.

RTV6 has received several questions on Facebook, through email and in calls to the newsroom about the phenomenon.

Conspiracy theorists have claimed that the trails left behind by jet aircraft have a more sinister purpose, referring to them as "chemtrails," claiming that they are spreading chemicals into the atmosphere.

But there is a logical scientific and meteorological explanation of what is happening in the atmosphere when a jet plane flies by.

"Contrail" is short for condensation trail. In short, a jet airplane emits exhaust and the trail behind it forms when hot, humid air mixes low temperature and low vapor pressure.

Contrails typically dissipate after a short period of time, but when certain atmospheric conditions exist, they can linger for hours, scientists say.

The National Weather Service said contrails linger when the upper atmosphere is moist, and they expand if there is an active jet stream overhead.

Those factors, in combination with the amount of air traffic over Indianapolis, explain why they are so prevalent over central Indiana when the right atmospheric conditions come together, as they did Monday.

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