Clearing the Skies
Predicting and Preventing Contrails
The white lines etched across the sky by airplanes are a type of airplane emission known as contrails and a team at Northrop Grumman is studying how to predict and prevent them — offering a new approach to reducing aviation’s impact on our skies.
If we can find a way to predict the conditions, then pilots can avoid creating them,” said Bill Deal, a Northrop Grumman engineering fellow who is on the team working with NASA’s Jet Propulsion Laboratory. “No one has tried to implement our unique approach.”
Condensation trails, or contrails, are created by an aircraft’s exhaust and can trap energy in the Earth's atmosphere.
Scientists have understood how to predict contrail formation since the 1940s. However, persistent contrails — which create cloud lines across the sky — are not as easy to predict.
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Tale of Tails
Scientists and engineers have documented contrails since high-altitude flights began in the1920s, but their impact remained largely unexplored . During World War II, increased aircraft use brought contrails into focus, highlighting formation flying.
Researchers wanted to learn why and how they formed. In the 1940s, they found that contrails form when the warm exhaust of an airplane engine mixes with the cold air at high altitudes.
“What is left behind is a visible trail of ice crystals and soot,” Bill said.
For the most part, contrails dissipate within minutes. But under the right conditions, they persist and evolve into aircraft-induced cirrus clouds (AICs), which reflect incoming sunlight or prevent outgoing radiation.
Predicting persistent contrails is challenging because they form only under specific atmospheric conditions, and not all of them form into AICs.
