A zap from the sun

I’ve always loved the science of lightning, hence, for instance the piece I wrote for the Observer. At the time I mentioned a theory linking cosmic rays to lightning strikes as, surprisingly, we really don’t know a lot about why lightning occurs. Now there’s some brand new (published today) research that suggests the Sun may be playing a part in the generation of lightning strikes by temporarily ‘bending’ the Earth’s magnetic field and allowing the shower of energetic particles that makes up cosmic rays to enter the upper atmosphere.

According to the IOP, ‘researchers at the University of Reading who have found that over a five year period the UK experienced around 50% more lightning strikes when the Earth’s magnetic field was skewed by the Sun’s own magnetic field. The Earth’s magnetic field usually functions as an in-built force-field to shield against a bombardment of particles from space, known as galactic cosmic rays, which have previously been found to prompt a chain-reaction of events in thunderclouds that trigger lightning bolts.’

Lead author of the research Dr Matt Owens said: ‘We’ve discovered that the Sun’s powerful magnetic field is having a big influence on UK lightning rates. The Sun’s magnetic field is like a bar magnet, so as the Sun rotates its magnetic field alternately points toward and away from the Earth, pulling the Earth’s own magnetic field one way and then another.’

In their study, the researchers 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. This change of direction can skew the Earth’s own magnetic field and the researchers believe that this could expose some regions of the upper atmosphere to more cosmic rays.

‘From our results, we propose that galactic cosmic rays are channelled to different locations around the globe, which can trigger lightning in already charged-up thunderclouds. The changes to our magnetic field could also make thunderstorms more likely by acting like an extra battery in the atmospheric electric circuit, helping to further “charge up” clouds,’ Dr Owens continued. The results build on a previous study which found an unexpected link between energetic particles from the Sun and lightning rates on Earth.

‘Scientists have been reliably predicting the solar magnetic field polarity since the 1970s by watching the surface of the Sun. We just never knew it had any implications on the weather on Earth. We now plan to combine regular weather forecasts, which predict when and where thunderclouds will form, with solar magnetic field predictions. This means a reliable lightning forecast could now be a genuine possibility.’

This paper can be downloaded from the IOP here.