Sun’s magnetic field sparks lightning on Earth

http://www.theguardian.com/science/2014/nov/19/sun-magnetic-field-lightning-earth

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Lightning is by its very nature unpredictable, but forecasting when and where it will strike has become easier following new research.

Space scientists have found that lightning strikes in the UK are being driven by changes that are occurring millions of miles away deep inside the sun. They found that the frequency of lightning strikes follows regular patterns that match the rotation of the sun’s magnetic field, increasing by up to 50% under certain circumstances.

This occurs because the sun’s magnetic field, which is known as the heliospheric magnetic field and is created by currents deep inside the star, warps the Earth’s own magnetic field.

Normally the Earth’s magnetic field helps to protect it from cosmic rays, high-energy particles that come from far outside the solar system, deflecting them around the planet.

However, as the sun’s magnetic field fluctuates, it bends the Earth’s own field directing the cosmic rays to the planet’s surface.

As they streak through the atmosphere, the rays are thought to create a pathway that allows the electrical charge built up in storm clouds to reach the ground.

A single cosmic ray is a proton that has energies millions of times higher than anything that can be produced in the Large Hadron Collider in Cern for example. When it collides with molecules in the atmosphere it produces a shower of secondary particles and a narrow channel of low electrical resistance allowing the charge from the cloud to travel to the ground.

Dr Matt Owens, a space weather expert at the University of Reading, said the findings could help to predict where, when and the type of lightning that might occur. “The solar magnetic field is very predictable - we’ve been doing it since the 70s, but never knew it had meteorological implications,” he said. “Adding that information into the Met Office’s weather forecasts could enable a better prediction of both lightning occurrence and intensity.”

It should also be possible to predict the type of lightning. “We saw an increase in the cloud-to-ground lightning strikes, which are the classic bolts that cause most damage and fatalities, when there were cosmic rays coming into the Earth’s atmosphere,” said Owens. “If there are not cosmic rays coming down, then the electrical charge might discharge into the clouds around it to produce more sheet lightning.”

Although such forecasts might not be able to predict the exact moment and spot where lightning will strike, it could allow scientists to estimate the probability of lightning over a certain area.

This information could prove essential for power companies and industries that use delicate electronic equipment. It could also help warn hill walkers to steer clear of dangerous areas.

Owens, whose work is published in the journal Environmental Research Letters, used satellite and Met Office data to show that between 2001 and 2006, the UK experienced a 50% increase in thunderstorms when the heliospheric magnetic field pointed towards the sun and away from Earth.

The sun rotates once every 27 days, so for half of that time the magnetic field is pointing towards the Earth and half the time it is pointing away. So for half a solar rotation you have enhanced lightning in the UK if there are a given number of thunder clouds or moisture in the air.