A recent study shows that cargo ships may be creating more lightning, and it was apparent to researchers that some physical processes were at play with the cargo ship – lightning relationships. So how does a cargo ship create lightning?
Seasonal lightning
A study published in the American Geophysical Union journal, Geophysical Research Letters, examined 12 years of global lightning stroke data (2005 to 2016) from the World Wide Lightning Location Network. Their analysis revealed that the density of lightning doubled over shipping lanes in the South China Sea and northeastern Indian Ocean compared to nearby, similar regions.
They also found that this lightning enhancement had some degree of seasonality. November to April was the dominant period for the Indian Ocean while April to December was most significant in the South China Sea.
The researchers finally hypothesize that aerosols (particulate matter) emitted from ship exhausts are the culprit.
Aerosols cause dense clouds
To understand how a cargo ship can affect lightning, it is important to understand the physical processes at play. Lightning is caused by glaciated storms. In other words, the storms are composed of a mixture of liquid drops, graupel, and ice crystals.
A fundamental premise of cloud development is that a “seed” or condensation nucleus is typically required for a cloud droplet (or ice crystal) to form. This is called heterogeneous nucleation. Cloud droplets and ice nuclei rarely form directly from the vapor phase without that “seed.” Thornton and his colleagues believe that the aerosols from ship tracks serve as condensation nuclei for cloud formation, which leads to deeper clouds able to become electrified.
The NASA satellite instrument MODIS (first image in the article cited above) reveals ship track clouds over the Pacific Ocean.
Evidence of human influence
These finding provides one of the clearest examples of a human perturbation to aerosol particles and lightning in an otherwise clean region. The researchers say that results indicate that the ship exhaust particles are, in fact, changing a tropical rainstorm into a thunderstorm—from no lightning to a storm with lightning, or adversely, the particles are increasing the vertical development of thunderstorms to an even more harder lightning than it would typically produce.
The researchers confirmed the last statements by comparing surface lightning data with radar data from NASA’s Tropical Rainfall Measuring Mission (TRMM), which had a satellite-borne weather radar. The radar can explore the vertical structure of the cloud in order to compare the depth of vertical liquid with ice particles.
This is just another piece in the puzzle of how human activity affects weather and climate.
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Source: Forbes
