Why is there less lightning over sea than land? Ocean spray

Hebrew University researchers discover why there’s less lightning in storms over oceans than on land: Coarse sea spray keeps lightning strikes away.

 Lightning over Jerusalem (photo credit: Prof. Daniel Rosenfeld)
Lightning over Jerusalem
(photo credit: Prof. Daniel Rosenfeld)

It had always been assumed that the rarity of lightning in ocean storms was due to cleaner air over the vast seas, but keen observations have shown that even highly polluted air is associated with reduced lightning at sea when sea spray aerosols are abundant. The known effects of thermodynamics and aerosols can well explain the thunderstorm activity over land, but it cannot over oceans.

“We found a major cause for such a difference between ocean storms and those on land.”

Prof. Daniel Rosenfeld

New research at the Hebrew University of Jerusalem (HU) has found that it is the larger, coarse sea spray that reduces the amount of lightning by as much as 90%, and that smaller particles (aerosols) increase lightning. The size of particles also affects rainfall. Their study clearly shows that the role of aerosols in clouds needs to be incorporated in climate models.  

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

Why is there more lightning over land than the ocean?

Prof. Daniel Rosenfeld and his doctoral student Zengxin Pan at HU’s Institute of Earth Sciences focused on the role of aerosols in controlling the amount of rain and lightning produced by clouds. Their research provides the explanation for why heavy ocean storms are accompanied by much less lightning than when a similar event occurs on land.

Rosenfeld’s findings, published in the prestigious journal Nature Communications under the title “Coarse sea spray inhibits lightning” fill in the gaps in previous theories about what was responsible for the difference in the number of lightning strikes between land and ocean storms.

 Prof. Daniel Rosenfeld  (credit: HEBREW UNIVERSITY OF JERUSALEM) Prof. Daniel Rosenfeld (credit: HEBREW UNIVERSITY OF JERUSALEM)

Tracking clouds over land and sea

The HU researchers in collaboration with scientists at China’s Wuhan and Nanjing Universities and the University of Washington were able to use satellite imagery to track clouds over land and sea. This was combined with lightning measurements from the Worldwide Lightning Location Network (WLLN) and with data that provided information on the number of aerosols in the clouds.

“We found a major cause for such a difference between ocean storms and those on land,” said Rosenfeld. “The effect of aerosols on clouds has been underappreciated. It needs to be incorporated into the models for better weather and climate prediction.”