Since ancient times, sailors have feared sudden lightning strikes that could set ships on fire and kill the crew. Today, this danger is minimal, but lightning itself may be even more common. Recent research shows that ocean-going ships can indeed create lightning.

The mechanisms of this lightning development are still debated. One theory is that aerosols released from ship exhaust alter the development of storms, leading to increased lightning strikes. It can also be hit by ships (long metal objects on the water plane).

In a new study published Earth and Space Science, and following an upcoming presentation at the 2023 AGU Annual Meeting in San Francisco, scientists are taking a new look at this question with additional data combining lightning strike locations with ship locations.

Study author Michael Peterson, a scientist at Los Alamos National Laboratory, said that while the data did not show direct strikes on ships, it did show a clear prevalence of lightning strikes very near shipping lanes rather than slightly further out. His conclusion: Ocean-going ships attract lightning strikes and, in some cases, possibly even cause lightning strikes.

Exciting meetings

The idea that shipping might increase the frequency of lightning strikes was first proposed in a 2017 paper that used data from a ground-based sensor network called the Worldwide Lightning Detection Network (WWLLN). The authors found that lightning intensity in some areas of the South China Sea and Indian Ocean close to shipping lanes was twice as high as in areas where the ship was not moving.

They hypothesized that aerosol particles from ship exhaust could alter convection in the storm, increasing electrification and causing more lightning strikes.

Peterson said he thought there might be a simpler explanation: Ships are large metal pillars.

They looked at the same WWLLN data as the authors of the 2017 paper and added shipping emissions data from the Global Database for Atmospheric Emissions Research (EDGAR), as well as data from transponders that track the location of ships around the world.

“Understanding the origin of lightning effects on ship tracks is an important and unsolved issue,” Yaqun Liu, an MIT doctoral student who studies lightning, wrote in an email. “Lightning in the wake of a ship is a great natural experiment to determine the physics,” said Liu, who was not involved in the new study.

By combining data from the ship’s transponders with WWLLN data, which records the locations of individual lightning strikes, Peterson found that lightning was 15 times more likely to occur near a ship at a distance of more than 2 kilometers (1.2 mi) and 66 times more likely than other lightning strikes. At a distance of 25 kilometers ( 15.5). shaft).

Peterson said the scale of the increase in strikes was unexpected. “It was something we honestly didn’t expect to find,” he said.

According to Peterson, this is a clear indication that the ships were struck by lightning. If the effects had been caused by aerosols from ship exhaust, they would likely have occurred in a more dispersed area rather than in the immediate vicinity of the ships, he said.

Location is important

Because ship transponder data is expensive, Peterson could only look at data from and near U.S. coastal waters. Thanks to EDGAR data, he gained insight into shipping routes around the world. Aerosols emitted from ships cause low-lying clouds to form, similar to aircraft trails that appear behind ships as they move. Therefore, although they do not reveal the locations of individual ships, they are representative of shipping traffic.

This dataset also showed that lightning strikes were more common near shipping routes than in nearby areas with less ship traffic, but only in the Bay of Bengal and the South China Sea. Other regions, such as the Red Sea, the Mediterranean and the US East Coast, did not experience an increase in lightning near shipping lanes.

Peterson said he thinks the Bay of Bengal and the South China Sea may contain clouds that are highly charged but do not produce many lightning strikes. Ships can provide extra thrust to warp these clouds and produce whistling electric shocks.

“You’re putting a metal object this long into an environment that already has strong electric fields, which could potentially trigger additional lightning strikes,” Peterson said.

Meanwhile, impacts elsewhere, such as off the US East Coast, may also be caused by ships, but not frequently enough to show patterns in the WWLLN data. A total of 36% of ships with transponder data examined in Peterson’s study experienced a near-direct or potentially direct lightning strike within 3 years. Some ships, like those navigating the turbulent waters of the Gulf of Mexico, have witnessed dozens or even hundreds of near misses.

Although Peterson’s study shows that metal ships likely cause lightning strikes, he notes that aerosols also likely play a role. Although their relative contributions are still unclear, both aerosols from marine diesel and the presence of ships themselves are likely to increase lightning near shipping lanes.

“Obviously, there is no simple or direct answer to the question of how lightning discharges are activated in a ship’s wake,” Liu said.

Better data on storm activity near ships could help clarify the issue, and Liu said that would also be important for the shipping industry. Although ships are designed to direct lightning strikes into the water without harming people, steering, navigation and other equipment can be damaged by the impacts, he said. Knowing where an attack may be more likely and what can be done to reduce the risk can help keep ships and passengers safe.