• Study : Ship Emissions Make Thunderstorms More Intense – gCaptain
    http://gcaptain.com/study-ship-exhaust-makes-thunderstorms-more-intense

    A new study mapping lightning around the globe finds lightning strokes occur nearly twice as often directly above heavily-trafficked shipping lanes in the Indian Ocean and the South China Sea than they do in areas of the ocean adjacent to shipping lanes that have similar climates.

    The difference in lightning activity can’t be explained by changes in the weather, according to the study’s authors, who conclude that aerosol particles emitted in ship exhaust are changing how storm clouds form over the ocean.

    The study published Sept. 7 in Geophysical Research Letters is the first to show ship exhaust can alter thunderstorm intensity. The researchers conclude that particles from ship exhaust make cloud droplets smaller, lifting them higher in the atmosphere. This creates more ice particles and leads to more lightning.

    The results provide some of the first evidence that humans are changing cloud formation on a nearly continual basis, rather than after a specific incident like a wildfire, according to the authors. Cloud formation can affect rainfall patterns and alter climate by changing how much sunlight clouds reflect to space.

    It’s one of the clearest examples of how humans are actually changing the intensity of storm processes on Earth through the emission of particulates from combustion,” said lead author Joel Thornton, a UW professor of atmospheric sciences.

    • L’article est en accès libre
      Lightning Enhancement Over Major Oceanic Shipping Lanes - Thornton - 2017 - Geophysical Research Letters - Wiley Online Library
      http://onlinelibrary.wiley.com/doi/10.1002/2017GL074982/abstract

      Abstract
      Using twelve years of high resolution global lightning stroke data from the World Wide Lightning Location Network (WWLLN), we 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 as compared to adjacent areas with similar climatological characteristics. The lightning enhancement is most prominent during the convectively active season, November-April for the Indian Ocean and April-December in the South China Sea, and has been detectable from at least 2005 to the present. 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. These persistent localized anthropogenic perturbations to otherwise clean regions are a unique opportunity to more thoroughly understand the sensitivity of maritime deep convection and lightning to aerosol particles.

      Plain Language Summary
      Lightning results from strong storms lifting cloud drops up to high altitudes where freezing occurs and collisions between drops, graupel, and ice crystals lead to electrification. Thus, lightning is an indicator of storm intensity and sensitive to the microphysics of cloud drop formation, interactions, and freezing. 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 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. 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. These shipping lanes are thus an ongoing experiment on how human activities that lead to airborne particulate matter pollution can perturb storm intensity and lightning.