How does lightning travel through the air? A new study led by Dr Chris Scott from the University of Reading, UK, suggests that high-energy particles accelerated by the solar wind could be part of the answer.
University of Reading scientists have discovered new evidence to suggest that lightning is triggered not only by cosmic rays from space, but also by energetic particles from the Sun. Image credit: University of Minnesota.
The solar wind consists of a constant stream of energetic particles – mainly electrons and protons – that are propelled from the Sun’s atmosphere at around a million miles per hour.
The streams of particles can vary in density, temperature and speed and sweep past Earth every 27 days or so, in line with the time it takes the Sun to make one complete rotation relative to the Earth.
The Earth’s magnetic field provides a sturdy defense against the solar wind, deflecting the energetic particles around the planet. However, if a fast solar stream catches up with a slow solar stream, it generates an enhancement in both the material and the associated magnetic field.
In these instances, the energetic particles can have sufficient energies to penetrate down into the cloud-forming regions of the Earth’s atmosphere and subsequently affect the weather that we experience.
In their study, Dr Scott and his colleagues analyzed data on the strikes of lightning over the UK between 2000 and 2005, which was obtained from the UK Met Office‘s lightning detection system.
The record of lightning strikes was compared with data from NASA’s Advanced Composition Explorer spacecraft, which lies between the Sun and the Earth and measures the characteristics of solar winds.
After the arrival of a solar wind at the Earth, the team 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.
“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,” said Dr Scott, the lead author of the paper published in the journal Environmental Research Letters.
“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.”
“In increasing our understanding of weather on Earth we are learning more about its important links with space weather,” said study co-author Prof Giles Harrison, also from the University of Reading.
“Bringing the topics of Earth Weather and Space Weather ever closer requires more collaborations between atmospheric and space scientists.”
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Scott CJ et al. 2014. Evidence for solar wind modulation of lightning. Environmental Research Letters, vol. 9, no. 5; doi: 10.1088/1748-9326/9/5/055004
