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2015-08-10 09:41:37
You know the saying lightning never strikes the same place twice ? Forget it. On a good night, one lake in Venezuela hosts thousands of lightning strikes every hour.
The phenomenon is known variously as the Beacon of Maracaibo, Catatumbo lightning or cue dramatic roll of thunder - the everlasting storm . That last one might be a slight exaggeration but where the Catatumbo River meets Lake Maracaibo there is an average of 260 storm days per year.
Here the night sky is regularly illuminated for nine hours with thousands of flashes of naturally produced electricity.
Summer storms are familiar to many of us but along the equator, where temperatures are higher, skies rumble throughout the year. DR Congo in Central Africa is known as the thunderstorm capital of the world where the mountain village of Kifuka, with 158 lightning flashes per square kilometre each year, was thought to be the most electric place on Earth. That was until more detailed data was analysed.
Did you know: lightning almost never strikes the north or south poles
In 2014, official figures from NASA revealed that the Brahmaputra Valley of far eastern India had the highest monthly lightning flash rate between April and May when thunderous activity ushers in the annual monsoon.
But Venezuela s Lake Maracaibo earned a place in the Guinness Book of World Records for highest concentration of lightning with 250 lightning flashes per square kilometre each year. The storms ease off in the dryer months of January and February and are most spectacular at the peak of the wet season around October. At this time of year, you can see an average of 28 lightning flashes each minute.
Experts have sought reasons for the area s uniquely intense storms for decades. In the 1960s it was thought uranium deposits in the bedrock attracted more lightning strikes. More recently, scientists suggested the conductivity of the air above the lake was boosted by the abundance of methane from oil fields below.
Neither theory has been proved though, so for now this record-breaking light show is attributed to a potent combination of topography and wind patterns.
A lot of the [lightning] hotspots are tied to features in the terrain - slopes of mountain ranges, curved coastlines, combinations of those, explains Dr Daniel Cecil from the Global Hydrology and Climate Centre s lightning team.
Having irregularities like that in the terrain can help generate wind patterns and heating or cooling patterns that would boost the likelihood of thunderstorms.
In North West Venezuela, South America s largest lake flows past the city of Maracaibo to join the Caribbean Sea. It lies in a fork of the Andes, so is surrounded on the other three sides by high mountain ridges. During the day, the hot tropical sun evaporates water from the lake and surrounding wetland. As night approaches, trade winds from the sea push this warm air into cold air cascading from the mountains. The hot air rises and dense cumulonimbus clouds form as towering plumes reaching up to 12 km (39,000 ft) high.
These distinctive storm clouds might look fluffy on the outside but inside a battle is raging. Where water droplets in the rising humid air collide with ice crystals in the cold air, static charges are produced and an electrical storm is unleashed.
The static electricity discharges in zig-zags of lightning that strike the ground, pass between clouds or flash inside them. The thunder itself is the shock wave of sound created when the heat of the lightning, which can be three times hotter than the surface of the sun, suddenly compresses the surrounding air. Alongside the sound and visuals are the special effects of heavy rain and hail.
The Catatumbo lightning is bright enough that it can be seen 400 km (250 miles) away and colonial sailors were said to use it for navigation. The force and duration of the storms have inspired many tales but eyewitness claims the lightning is multi-coloured are a trick of the light.
As it passes through dust or moisture, portions of the white light are absorbed or diffracted making it appear a different colour. There are also reports of it being silent but this is another perspective trick. The sluggish speed of sound compared to light means thunder may not reach distant spectators.
If you re wondering how scientists record all of their lightning data you can put the idea of kites and keys out of your mind. Benjamin Franklin might have famously proved the electrical nature of lightning with that equipment but in the modern age more sophisticated technology has allowed us to observe from a safe distance an altitude of 402.5km (250 miles) to be exact.
For 17 years, instruments on board the Tropical Rainfall Measuring Mission (TRMM), a joint project between NASA and the Japan Aerospace Exploration Agency, collected a wealth of meteorological data as the satellite orbited the Earth. This included the Lightning Image Sensor which recorded flashes of light in tropical skies. With this data scientists were able to produce a map of the world s lightning hotspots.
To me the next generation of weather satellites is especially exciting, says Dr Cecil, as TRMM finally runs out of fuel and returns to Earth.
In the next few years, there are plans for lightning mapping instruments on a few different geostationary satellites placed over different parts of the globe. These will give us continuous measurements of lightning activity, instead of the brief snapshots we have seen from previous satellites in low-earth orbit.
The ability to predict storms is becoming increasingly important as the global population grows, particularly in developing countries where people are more likely to work outdoors and lack sufficient lightning protection. To help us understand where in the world lightning strikes, storms are also analysed from below.
The World Wide Lightning Location Network (WWLLN) comprises sensors based at 70 universities and research institutions that pick up the very high frequency signals emitted by lightning. Prof Robert H. Holzworth, who leads the network from the University of Washington, says the ground based observations compliment the satellite data.
The ground based systems can see the whole world instantaneously, and continuously, something no satellite system past, present or future can do. On the other hand, to be recorded electrically using VLF radio waves requires the more powerful lightning stroke energies. So, the global ground based systems do not see all the little strokes in the clouds, which can be seen by the satellites.
For any aspiring storm chasers that can t quite give up the mug of cocoa and cosy blanket, the WWLLN produce a real-time map of lightning strokes around the globe.
For the brave, tours to Lake Maracaibo are available.