Using LIDAR to study the impact of contrails on climate

In the skies over Virginia it is common to see contrails, cloud-like strips of condensed water left behind by aircraft at high altitude.

Some dissipate within minutes, but depending on the weather or time of day, some can remain for hours or develop into wispy cirrus clouds. Because of that, there is uncertainty about how exactly contrails affect the environment, and scientists are studying how they may be trapping heat in the atmosphere.

To do that, researchers at NASA Langley have partnered with GE Aerospace to further examine the effects of contrails. Using LIDAR technology, or light detection and ranging, researchers used a power laser attached to the bottom of a research plane to capture cross-sections of a contrail left by a GE aircraft. That allowed them to see what structures are left behind that may not be visible from the ground.

The LIDAR creates a two-dimensional curtain to measure water vapor, so researchers can see where the atmosphere is more saturated. With those images, scientists can see how thick contrails are and what conditions create the most disruptive versions.

"We like to think of these contrails as just two circles of ice, and it's a lot more complicated than that," said Rich Moore, research scientist and principal investigator of the program. "For the first time, we're able to sort of peel back that veil and see some of the underlying complexity."

Contrails are very bright white, and in many cases they can reflect sunlight, which typically cools the atmosphere, said Cassi Miller, senior engineer for GE's Revolutionary Innovation for Sustainable Engines (RISE) program. However, when contrails form or stick around for nightfall, she said they can cause issues. Because there's no more sunlight to reflect, they begin trapping heat.

What kind of surface is below contrails, such as sea or land, can affect them as well, but Miller said the experiments with NASA and GE will help create more definitive data.

"A lot of people look up in the sky and some days you see contrails, some days you do not. It's kind of hit or miss with weather, but most people don't think about their climate impact," Miller said. "As an industry and in collaboration with atmospheric scientists, there is a general growing consensus that they have a warming impact on the climate. There's a lot of uncertainty around that.

"People are familiar with (carbon dioxide) emissions, right? How does the impact of a contrail compare? Is it the same scale? Is it a different magnitude? That's part of what we're trying to figure out in this campaign."

With the experiment, Moore said data can be used to map where conditions for contrails can be the strongest and create paths where aircraft can avoid them. Tests will also be used for research into more sustainable aircraft engines.

"We're very interested and concerned about fuel burn and aviation's (carbon dioxide) emissions, which we know impact climate. In addition to that, we're also starting to become much more concerned about contrails," Moore said.

"The reason for that is that the global modelers today tell us that the climate impact from contrails and aviation-induced cirrus clouds is about the same warming impact as the past century's worth of aviation—since the beginning of the jet age.

"And so, of course, (carbon dioxide) is with us for 100 years or so after we admit it, so we're very interested in improving fuel efficiency and continuing to make airlines and airframes and engines more efficient," she added. "But we also need to be concerned about, at some point, reducing contrails."

Eliza Noe is Climate and Environment reporter with The Virginian-Pilot. Distributed by Tribune Content Agency, LLC.