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Understanding lightning

From large-scale sporting events to North Sea helicopter operations, lightning is a major hazard that's difficult to forecast. But thanks to the Met Office's state-of-the-art prediction models, it's now possible to pinpoint where it will strike. And for developing countries around the world, that's helping to save lives.

Power cuts. Travel chaos. Even danger to lives. Lightning can have a huge impact on the UK, but it is notoriously difficult to predict. While in the past it's been possible to identify prime conditions for thunderstorms to form - areas of atmospheric instability - anticipating where lightning might actually strike had been a huge challenge. In fact, estimations could typically span hundreds of miles.

But now - with developments to the numerical weather prediction (NWP) model - the Met Office can produce much narrower, and therefore far more practical, forecasts. Using a complex set of mathematical equations, the model analyses real-world weather data and predicts atmospheric instability, enabling forecasters to isolate specific areas where lightning will occur.

"Previous predictions could involve an area typically the size of Wales, but today location accuracy could be down to as little as 30 to 50 miles," explains the Met Office's Dr Jonathan Wilkinson, who specialises in cloud microphysics modelling. Having an accurate, localised picture of potential strikes means that both public organisations and private businesses - from the emergency services to aviation and rail industries - can put plans in place to swiftly deal with the effects of lightning - keeping the country moving, and safe.

London 2012: a global stage

When it came to putting the model into practice for the first time, a prestigious opportunity presented itself. On 27 July 2012, around 80,000 spectators gathered in London for the Olympic Games opening ceremony. It involved a Red Arrows flypast, a towering copper cauldron and a surprise stunt involving a helicopter, a parachute and the Queen - all of which would have been at risk if lightning were to strike.

On the day of the ceremony, Met Office forecasters contacted Jonathan's team, having spotted lightning on the other side of the English Channel. Coupled with the light rain that had fallen near the stadium that afternoon, this suggested potential weather hazards could disrupt festivities. Fortunately, thanks to the NWP model, the team was able to quickly and confidently confirm that lightning was unlikely to occur over London that evening.

Taking flight

The research has also proved critical to helicopter operations. North Sea helicopter pilots face a very particular challenge known as 'helicopter triggered lightning' - strikes that happen due to the presence of the aircraft, despite there being no observed lightning activity in the area.

The Met Office has been working closely with pilots to calculate the conditions likely to create thunderstorms, and created a tool that gives access to weather data via a web browser. This enables pilots to establish the probability of strikes along a particular route and the degree of accuracy it provides means they can amend flight paths to avoid risk, rather than having to abandon outings entirely. With hundreds of costly helicopter movements across the North Sea every day, the service has proved invaluable.

Going global

Benefits are being felt internationally, too, such as in Manila in the Philippines. As one of world's most densely populated cities, it is particularly vulnerable to intense rain and thunderstorms - and the devastating flooding that can be a direct result. Meanwhile, on the other side of the globe in a much less built-up area, research has been of great benefit to fishermen on Lake Victoria - a notoriously challenging environment, where squalls have frequently proved fatal.

In remote regions, access to communications can be limited and people often rely on mobile phones for weather updates. So while forecasting thunderstorms is vital, it's only part of the picture - and getting warnings to the right people at the right time is also critical. That's why the Met Office works closely with international weather authorities, either providing data or helping them generate their own forecasts. Armed with this information, regional forecasters can then send out storm alerts locally, providing warnings that could ultimately save lives.

The lightning of the future

Jonathan's team is now turning its attentions to future global climates; a hot topic, as recent research suggests climate change could bring about increased lightning activity. Met Office scientists have been examining Convective Available Potential Energy (CAPE) and investigating the potential for more lightning in warmer weather. But the next step is to establish exactly where strikes might occur.

"Rather than just saying 'we think there will be more lightning in warmer climates', we want to know specifically whether this will happen across the whole of the UK, or the South East corner where we expect it to get warmest," explains Dr Wilkinson. "Then we want to understand the precise effects on a global scale."

What is lightning?

Lightning is a large electrical spark caused by electrons moving from one place to another. Electrons cannot be seen, but when they are moving extremely fast, the air around them glows, causing the lightning flash. The actual streak of lightning is the path the electrons follow when they move.

What causes lightning?

The answer lies in the clouds. Lightning naturally occurs in areas of atmospheric instability - when warm air collects beneath areas of colder air. This causes deep cumulonimbus clouds to form, in which ice and hail accumulate. When they collide, hail develops a negative charge, while ice remains positive. In the right set of circumstances, this energy is discharged towards the Earth in what we know as a bolt of lightning.

Man can also trigger lightning. As a helicopter flies and the rotary blades spin, they produce a strong charge. When they land, this is usually released into the earth.

But if, when flying, they meet an area of thundercloud with its own electrical charge, a static discharge happens - which can actually bring about a lightning strike.