Lightning is an indicator of storm intensity. In a recent study 12 years of high-resolution global lightning stroke data from the World Wide Lightning Location Network (WWLLN) was used to show that lightning density is enhanced by as much as twice directly over shipping lanes in the northeastern Indian Ocean and the South China Sea as compared to adjacent areas with similar climatological characteristics.
The World Wide Lightning Location Network is the longest running global lightning network, with coverage beginning in August 2004. Estimates of shipping emissions were calculated from the Emissions Database for Global Atmospheric Research (EDGAR) available as monthly averages for the year 2010. These emissions estimates use fuel usage statistics based on real-time ship information (number, size/type, heading, speed, etc.) from the automatic identification system (AIS) required on all marine vessels for collision avoidance. The shipping AIS data indicate that most vessels traversing the northern Indian Ocean follow a very narrow, nearly straight track between the southern end of Sri Lanka and the northern tip of Sumatra. East of Sumatra, the shipping lane runs southeast through the Strait of Malacca, rounding Singapore and extending northeast across the South China Sea. Aerosol particle emissions in these shipping lanes are larger by an order of magnitude or more than in other shipping lanes in this region.
The lightning enhancement has been detectable from at least 2005 to the present. It is suggested that emissions of aerosol particles by maritime vessel traffic lead to cloud development causing more cloud water to be transported to high altitudes, where electrification of the storm occurs to produce lightning.