Northern Ireland

Why did some parts of NI have lightning but no thunder?

Generic lightning photograph Image copyright Elvis
Image caption Can there be lightning without thunder?

They go together like Lennon and McCartney and fish and chips. Thunder and lightning - you can't have one without the other.

Sometimes though, like in parts of Northern Ireland on Friday morning - lightning was seen but no thunder was heard.

The reason? This is where it gets technical. It is either because the thunder is too far away or because the atmospheric conditions lead to sound bending upwards and away from the Earth's surface.

The Met Office explains: " When lightning strikes the narrow channel of air, through which it travels, it reaches temperatures of up to 30,000°C almost instantly.

"This intense heating causes the air to rapidly expand outward into the cooler air, creating a rippling shockwave which we hear as a rumbling clap of thunder."

"Loud crack or low rumble"

"Depending on its formation and location, thunder claps can be heard as either a sudden, loud crack or a low, long rumble," the Met Office adds.

"Thunder lasts longer than lightning because of the time that it takes for the sound to travel from different parts of the lightning channel."

Image copyright Chris Kinkead
Image caption Lightning caught on camera in Newtownabbey

Thunderstorms develop when the atmosphere is unstable - with warm air sitting underneath a layer of much colder air. As the warm air rises, it cools and condenses, forming small droplets of water.

These particles of water rattle around in the quickly forming cloud. Rising on the warm air, they then freeze into ice particles at the higher altitudes, and then fall as hailstones once they reach a certain size.

Eventually the cloud becomes "charged" with energy. What this means is there is a negative charge at the base of the cloud, where the hail collects, and a positive charge at the top of the cloud, with lighter ice crystals.

The attraction of the negative charge in cloud to the Earth's surface becomes too strong and boom - you get a flash of lighting.


Lightning fact file

  • On average a bolt of lightning lasts for about one 10,000th of a second
  • Lightning travels through the air at around 270,000 mph - that's around 75 miles every second
  • Lightning is hotter than the surface of the sun reaching temperatures of around 30,000 °C

Thunder is always produced by a lightning strike but there is a time delay between the two.

That's because light travels at a speed of 299,792,458 metres per second, while the speed of sound is a much more pedestrian 340.29 metres per second.

Image copyright James T. Clarke
Image caption Stormy skies over Fisherman's Quay, Carrickfergus

On Friday, many of the lightning strikes took place off the south east coast of County Down.

As the sound waves came onshore, many would have been deflected upwards into the atmosphere by the Mourne mountains.

So the next time you hear thunder and see lightning, you'll know all the science behind it!

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