Study: Air pollution from ocean vessels increasing lightning strikes over shipping lanes

Even small absolute increases in remote marine aerosol particles due to human activities could have a substantial impact on storm intensity and lightning, according to a new report published in the scientific journal Geophysical Research Letters.    A new study recently published in the scientific journal Geophysical Research Letters claims that an increase in lightning strikes occurring over major oceanic shipping lanes is being caused by maritime vessel traffic.
   In a research letter first published Sept. 14, the four authors, using 12 years of high-resolution global lightning stroke data from the World Wide Lightning Location Network (WWLLN), say they have managed to show that lightning density “is enhanced by up to a factor of two” directly over shipping lanes in the northeastern Indian Ocean and the South China Sea compared to adjacent areas with similar climatological characteristics but significantly less vessel traffic.
   The doubling of lightning mostly occurs from November to April in the Indian Ocean and April through December in the South China Sea, and has been detectable from at least 2005 to the present, according to the study.
   “We hypothesize that emissions of aerosol particles and precursors by maritime vessel traffic lead to a microphysical enhancement of convection and storm electrification in the region of the shipping lanes,” the authors said.
   “We find that lightning is nearly twice as frequent directly over two of the world’s busiest shipping lanes in the Indian Ocean and the South China Sea,” the report states. “The lightning enhancement maximizes along the same angular paths ships take along these routes and cannot be explained by meteorological factors, such as winds or the temperature structure of the atmosphere.
   “We conclude that the lightning enhancement stems from aerosol particles emitted in the engine exhaust of ships traveling along these routes,” the authors explained. “These particles act as the nuclei on which cloud drops form and can change the vertical development of storms, allowing more cloud water to be transported to high altitudes, where electrification of the storm occurs to produce lightning.”
   The authors, Joel A. Thornton, Katrina S. Virts, Robert H. Holzworth and Todd P. Mitchell of the University of Washington at Seattle, say that shipping lanes can be looked at as an ongoing experiment in how human activities that lead to airborne particulate matter pollution can influence storm intensity and, therefore, lightning frequency.
   The researchers say they considered 1.5 billion lightning strikes that occurred over a 12-year period between 2005 and 2016, and found that the strikes that happened over the ocean were concentrated along shipping lanes, particularly the lanes from Singapore and the western part of Malaysia that head north-east across the South China Sea, as well as those from the south of Sri Lanka to the northern entrance of the Straits of Malacca and down the straits to Singapore.
   “[L]ightning occurrence over the shipping lanes is clearly and persistently enhanced compared to the background rates in the adjacent reference regions,” the study determined. “Our findings suggest that even small absolute increases in remote marine aerosol particles due to human activities could have a substantial impact on storm intensity and lightning.”