Lightning: how is it detected?
Yesterday saw thunder and lightning affect many northern and western parts of the UK, as cooler air clashed with warm, humid air, causing the atmosphere to destabilise.
This sent intense, thundery downpours northwards across the country, with some places seeing a lot of rain in a short space of time.
However, the more visual element of yesterday’s weather was the frequent lightning seen in some places. The image below shows that 5,736 lightning strikes were recorded across the British Isles yesterday, with each one plotted as a cross on the map.
You can see that the lightning was concentrated across Wales, before spreading across coastal parts of north west England, south west Scotland, as well as the Isle of Man.
Lightning in pictures
Last night, I had lots of pictures sent to me on Twitter showing the lightning – some of which you can see below.
— Liverpool Weather (@liverpoolweath) May 19, 2014
So this is happening outside my window…… pic.twitter.com/7DFgSYJQTt
— Laura Jennings (@Laura_Jennings) May 19, 2014
How is lightning detected?
When lightning strikes occur, pulses of electromagnetic energy are created, spreading out in all directions.
These pulses, known as sferics, have a very low frequency (VLF), which is outside the range of what we are able to see and much lower than the frequency of normal radio waves.
These VLF waves are capable of travelling large distances because they are reflected between the surface of the earth and a layer of the upper atmosphere called the ionosphere.
When a lightning strike occurs, each sensor will record the sferic at a slightly different time as the distance between each sensor and the point at which the lightning strike originated will vary.
The network of sensors, connected to a central computer at Met Office HQ, then cross-references the time each lightning strike took to be detected by each sensor, and is then able to triangulate the point at which it took place – a process called Arrival Time Difference (ATD).
Once a lightning strike has been detected, the information can be plotted on a map to show when and where they have taken place.
Is any more lightning on the way?
The next few days will continue to see low pressure interact with some warm, humid air from the near continent.
This means that further heavy downpours are likely, accompanied by thunder and lightning at times.