Coarse sea spray keeps lightning strikes away

As the world grapples with the cataclysmic events associated with climate change, it is increasingly important to have accurate climate models that can help predict what might lie ahead. 

Research at the Hebrew University of Jerusalem (HU)’s Institute of Earth Sciences, led by Professor Daniel Rosenfeld and his doctoral student Zengxin Pan, focused on the role of small particles (aerosols) in controlling the amount of rain and lightning produced by clouds. Their research has been able to explain why heavy ocean storms are accompanied by much less lightning than when a similar event occurs on land.  They identified that it is the larger, coarse sea spray that reduces the amount of lightning by as much as 90%, whereas smaller aerosols increase lightning. The size of particle also affects rainfall.  Their work clearly shows that the role of aerosols in clouds needs to be incorporated in climate models. 

Rosenfeld’s findings, published in Nature Communications, fill in the gaps in previous theories about what was responsible for the difference in lightning between land and ocean storms. It had always been assumed that the dearth of lightning in ocean storms was due to cleaner air over the ocean.  However, keen observations had already shown that even highly polluted air is associated with reduced lightning at sea when sea spray aerosols are abundant. 

The HU researchers in collaboration with scientists at Wuhan and Nanjing Universities in China, and the University of Washington, were able to use satellite imagery to track clouds over land and sea.  This was combined with lightening measurements from the Worldwide Lightning Location Network (WLLN) and with data that provided information on the amount of aerosols in the clouds.   "We found a major cause for such a difference between ocean storms and those on land," shared Rosenfeld. "The effect of aerosols on clouds has been underappreciated.  It needs to be incorporated into the models for better weather and climate prediction."