Tuesday, November 18, 2014

Sun boosts UK lightning strikes


The number of lightning strikes across the UK has been significantly affected by solar activity, according to new research.


Scientists say the Sun's magnetic field is bending the Earth's own field, increasing our exposure to cosmic rays.


These rays are believed to increase the number of thunderclouds and trigger lightning bolts in some locations.


Over five years, the UK experienced 50% more strikes when the Earth's magnetic field was affected by the Sun.


Fields of influence


The manner is which lightning bolts are triggered has long puzzled scientists as the air is known to be a good insulator of electricity.


Something else needs to come into play to conduct the electrical charges built up in thunder clouds down to the ground.


Since the 1990s, researchers have speculated that the magnetic activity of the Sun could be linked to lightning on Earth.


Current theories hold that high energy particles called galactic cosmic rays provide the necessary link that lets the current flow into a lightning bolt.


This latest work suggests that the orientation of the Sun's magnetic field is playing a significant role in the number of strikes.


The researchers believe the field is like a bar magnet, so as our star spins around sometimes the field points towards the Earth and sometimes away.


'What we found was there is significantly more lightning in the UK when the field is pointing towards the Sun than when its pointing away which was surprising,' said Dr Matt Owens from the University of Reading, the lead author on the study.


'What we think is happening is that the Sun's magnetic field is pulling or pushing on the Earth's field and that's letting energetic charged particles down into the atmosphere at different locations and the idea is that these actually trigger lightning.'


'For lightning, you need a thin conducting channel like a wire, and galactic cosmic rays can provide this thin column of ionisation in the atmosphere.'


The researchers found that over a five year period between 2001 and 2006, the UK experienced a 50% increase in thunder and lightning rates when the solar magnetic field was pointed away from the Earth.


In Summer, the rates were higher, with an almost doubling of lightning strikes in July compared to when the magnetic field was pointing in the other direction.


Because of good quality records, the scientists confined their work to the UK. They believe that the same effect is playing out over the globe but with different results, so while lightning might increase over Britain, it may have decreased over Canada or Siberia.


Lightning forecast


While the researchers admit that the mechanics of how cosmic rays might trigger lightning is still a theory, they believe that their discovery of an association with the movements of the Sun's magnetic fields, could lead to better predictions of thunder and lightning events.


As the nature of the Sun's magnetic fields are well known, meteorologists could incorporate this information into weather forecasts.


'It has real implications,' said Dr Owens,


'If you can get a weather forecast good to a week ahead then yes I think we could say something about lightning rates a week ahead as well.'


Recent research has also focussed on how climate change is likely to increase the amount of lightning strikes around the world. Dr Owens believes that the mechanism that his study identifies still holds, regardless of the temperature.


'If you heat up the atmosphere you've got more convection, more water vapour, you get more thunderclouds,' he said.


'If you've got more thunderclouds, you get more lighting but I still think the triggering of that lightning could be dependant upon the Sun and its magnetic field.'


The researchers now want to extend their work to look at longer historical records to see if the correlation still stands.


According to Dr Owens, some scientists are keen to take a more 'Benjamin Franklin' approach to prove the theory.


'The fundamental lightning triggering experiments are difficult to do in the lab and difficult to measure in situ,' he said.


'Some of my colleagues have been trying to launch charge sensors on balloons, through thunder clouds - it makes our health and safety officers sweat!'


The study has been published in the journal Environmental Research Letters.


Follow Matt on Twitter @mattmcgrathbbc.