UW researchers find container ships may create their own lightning

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Maybe you've seen some of the footage of giant container ships, loaded down with tons of cargo, rocking and rolling in a massive lightning storm as they plow through treacherous ocean waters. But what may be a surprise to you and to those manning the ships: the very vessel trying to safely navigate the storm is causing that storm to strengthen.

A new study from the University of Washington has tied lightning frequency to the busy shipping lanes that intersect our ocean waters. To make the best time (and money!), cargo ships all take the same routes to get from point A to point B, creating oceanic super-highways that criss-cross the globe.

UW Earth and Space Sciences Professor Robert Holzworth runs the World Wide Lightning Location Network, which maps lightning strikes all over the earth. When strange, long tracks of lightning strikes showed up in his data, he thought there might be a problem.

"Because it looked unnatural," Holzworth said.

Lightning should show up in random clumps, not in long, straight lines.

Fellow UW researcher, Atmospheric Sciences Professor Joel Thornton, worked with him to get to the bottom of the mystery. Thornton's group had a hunch:

"The fact that these were nice, straight lines that laid on top of where ship tracks were, it was clear we had an interesting result," Thornton said.

(Photo in Tweet: Thornton et al/Geophysical Research Letters/AGU)

When exhaust is emitted into the atmosphere, the particles act as "cloud seeds." Water droplets will grow on them, clouds will form, and this impacts weather. Professor Holzworth recalled an example where a lack of exhaust very obviously reduced the cloud cover over the United States: In the aftermath of the Sept. 11 attacks, when all air traffic was grounded.

"They cut off all the air traffic, you could look at images of the U.S. at that time and the clouds went away," Holzworth said. "All the contrails disappeared."

So we know that exhaust and pollutants lead to cloud formation, but how do we make the jump to lightning? In a recent scientific article, Professors Thornton and Holzworth surmise that because the exhaust particles are so small and the cloud droplets that form around them are so light, that they travel higher into the colder part of the atmosphere. That's where they form ice - and that leads to lightning.

In fact, the lightning data has noted that strikes double over the shipping lanes near Asia and the Indian Ocean.

"They're potentially enhancing their chance of getting struck (by lightning) by a factor of two," Thornton said.

Since this is fresh science, Professor Thornton doesn't think the sailors realize their own pollution leads to dangerous thunderstorms. But is this a problem in the Northwest, too? We don't have to deal with lightning off of the coast of the Pacific Northwest, as it's not a naturally stormy area anyway. For this phonomenon to occur, you need to have a lot of lightning available already.

Another reason for all of the exhaust over the shipping lanes? There are few regulations. But that will change in 2020. Currently, ships in international waters can burn the dirtiest, cheapest fuel, but ships will be required to use cleaner fuel in 2020.

"We should have an immediate response in lightning if the hypothesis is correct," Thornton said.

So, if it's clear that exhaust emissions lead to more lightning, does this become a political point of contention? Should the U.S. do even more to regulate pollution than we already do?

"I don't know the answer to that," Holzworth said. "That's the cool thing about the science we do. We're looking for an understanding at the fundamental level of a natural phenomenon. So what Joel and I and the rest of our team have done is to go out and say, 'What's the physical background and understanding of this phenomenon, and the politicians can take it wherever it leads."

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