High-speed solar winds trigger lightning on Earth

Lightning on Earth is triggered not only by cosmic rays from space but also by energetic particles from the Sun, according to a new study that can help predict the severity of hazardous weather events weeks in advance.
Researchers at the University of Reading found a link between increased thunderstorm activity on Earth and streams of high-energy particles accelerated by the solar wind, offering compelling evidence that particles from space help trigger lightning bolts.
They found a substantial and significant increase in lightning rates across Europe for up to 40 days after the arrival of high-speed solar winds, which can travel at more than a million miles per hour, into the Earth's atmosphere.

Although the exact mechanism that causes these changes remains unknown, the researchers propose that the electrical properties of the air are somehow altered as the incoming charged particles from the solar wind collide with the atmosphere.
After the arrival of a solar wind at the Earth, the researchers showed there was an average of 422 lightning strikes across the UK in the following 40 days, compared to an average of 321 lightning strikes in the 40 days prior the arrival of the solar wind.
The rate of lightning strikes peaked between 12 and 18 days after the arrival of the solar wind.

The results could prove crucial for weather forecasters, since these solar wind streams rotate with the Sun, sweeping past the Earth at regular intervals, accelerating particles into Earth's atmosphere.

As these streams can be tracked by spacecraft, this offers the potential for predicting the severity of hazardous weather events many weeks in advance, researchers said.
"Our main result is that we have found evidence that high-speed solar wind streams can increase lightning rates. This may be an actual increase in lightning or an increase in the magnitude of lightning, lifting it above the detection threshold of measurement instruments," lead author of the study, Chris Scott, said.

"Cosmic rays, tiny particles from across the Universe accelerated to close to the speed of light by exploding stars, have been thought to play a part in thundery weather down on Earth, but our work provides new evidence that similar, if lower energy, particles created by our own Sun also affect lightning.
"As the Sun rotates every 27 days these high-speed streams of particles wash past our planet with predictable regularity. Such information could prove useful when producing long-range weather forecasts," Scott said.
The study was published in the journal Environmental Research Letters.