From Africa to Scotland

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It sounds more like folklore than science, but meteorologists have discovered that lightning in Africa could be a warning of cloudy skies in Britain.

Thunderstorms over central and east Africa were found to create an electrical charge in the sky above Scotland, 8,000 miles away.

The researchers believe this "fair weather electric field", carried around the globe in the upper atmosphere, could influence the weather by triggering cloud formation. 

The finding has been hailed as a real-life example of the "butterfly effect", in which a seemingly minor event has a big impact elsewhere.

This shows just how intricate the climate system is, said Professor Giles Harrison, head of the department of meteorology at the University of Reading and leader of the research team.

There are unexpected and subtle links between one place and another many miles away.

There is a current that flows from the tropical thunderstorms into the ionosphere [upper atmosphere] and back down again to regions where there clear skies.

It can be thought of as a kind of giant electric circuit looping around the Earth where the thunderstorms around the equator are a kind of battery, and the wires are formed by the ground and the ionosphere. Areas where the skies are clear cause small leakages from that circuit.

Professor Harrison and his colleagues, whose work is published in the Institute of Physics scientific journal Environmental Research Letters and Environmental Research Web, have now been able to explain a phenomenon that has baffled scientists since 1753, when Louis-Guillaume Le Monnier, the French natural scientist, discovered that the atmosphere could become electrified even on clear days,

Professor Harrison analysed 60 years of Met Office data on the electrical field above Lerwick in Shetland, where there is little pollution to interfere with the electric signal.

He found that peaks in the electric field at times when skies were blue, which had never been explained before, correlated with times of thunderstorms in Africa.

There were also smaller peaks that coincided with storms in Australia and America, indicating a global circuit of electrical activity.

The professor has also shown that electrical activity in the atmosphere can help turn water droplets in clouds into larger drop, increasing the chances of rain clouds and rain.

He added: "We have found that it causes a small amount of charging on the edge of clouds. It is quite interesting that electrified clouds can be forming so far away from thunderstorms."

Richard Gray - Telegraph