The amount of lightning in thunderstorms over land is typically greater than that seen in thunderstorms over tropical oceans. The reduced frequency of lightning over the oceans is a phenomenon that has thus far eluded a convincing explanation. To get to the bottom of this, a collaborative team of researchers from Wuhan University and Nanjing University in China, The Hebrew University of Jerusalem, and the University of Washington, Seattle, USA, analyzed weather, aerosol, and lightning activity data from over Africa and the continent’s adjacent oceans.

Lightning is a spark of electricity caused when two electrically charged regions neutralize each other. Lightning is often associated with storm clouds, which are turbulent masses of water droplets. In such clouds, water droplets that are drawn to the top of the cloud by updrafts freeze. When these are eventually pushed downward by a downdraft, the frozen droplets collide with uprising liquid droplets. As the ice and water collide, electrons are stripped off the molecules, resulting in the electrification of the cloud. In their recent study, published in Nature Communications, the authors share how coarse marine aerosols, such as salt from sea spray, can reduce the frequency of lightning. They also show how in
contrast, fine aerosols, which are more common over land, promote cloud electrification. Large aerosols such as salt particles weaken convection (updrafts and downdrafts) within the cloud, and this promotes droplets to fall as rain instead of rising upward to form ice. If fewer ice particles form, there is less chance for cloud electrification.

These findings not only improve our understanding of why lightning is less common over the ocean, but also how lightning, storms, and atmospheric circulation may be impacted by climate change in the future.

About the researchers: This project was a collaboration between many researchers including Wei Gong, Zengxin Pan, Feiyue Mao, Lin Zang, Xin Lu, and Jianhua Yin of Wuhan University, Daniel Rosenfeld and Avichay Efraim of The Hebrew University of Jerusalem, Yannian Zhu of Nanjing University and Joel A. Thornton and Robert H. Holzworth or University of Washington, Seattle.

Managing correspondent: Arianna Lord
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