WMO CERTIFIES MEGAFLASH LIGHTNING EXTREMES

A World Meteorological Organization (WMO) committee of experts has established two new world records for the longest reported distance and the longest reported duration for a single lightning flash in, respectively, Brazil and Argentina.

Background

• The first megaflash event, which set the record for longest-distance flash, was more than seven times larger than the minimum criteria for a megaflash and was twice as large as the previous record-holder.
• The flash developed in spring 2018 in southern Brazil north of Porto Alegre, then spread both east and west simultaneously, stretching more than 440 miles from west to east as the crow flies.
• The previous record for the longest recorded distance for a single megaflash event was just under 200 miles across, set in Oklahoma in June 2007.

The mechanism behind lightning

• Lightning is an electrical discharge caused by imbalances between storm clouds and the ground, or within the clouds themselves. Most lightning occurs within the clouds.
• “Sheet lightning” describes a distant bolt that lights up an entire cloud base. Other visible bolts may appear as bead, ribbon, or rocket lightning.
• During a storm, colliding particles of rain, ice, or snow inside storm clouds increase the imbalance between storm clouds and the ground, and often negatively charge the lower reaches of storm clouds.
• There are three categories of lightning-
  • intracloud (IC), which is flashes within a cloud
  • cloud to cloud (CC), where lightning jumps from one cloud to another
  • cloud to ground (CG), where lightning strikes from the ground. This is the most well understood kind of strike and the riskiest to life.
• Lightning is extremely hot—a flash can heat the air around it to temperatures five times hotter than the sun’s surface.
• Thunder: This heat causes surrounding air to rapidly expand and vibrate, which creates the pealing thunder we hear a short time after seeing a lightning flash.

How does this current reach the Earth from the cloud?

• While the Earth is a good conductor of electricity, it is electrically neutral. However, in comparison to the middle layer of the cloud, it becomes positively charged.
• As a result, about 15%-20% of the current gets directed towards the Earth as well. It is this flow of current that results in damage to life and property on Earth.
• There is a greater probability of lightning striking tall objects such as trees, towers or buildings. Once it is about 80-100 m from the surface, lightning tends to change course towards these taller objects.
• This happens because air is a poor conductor of electricity, and electrons that are travelling through air seek both a better conductor and the shortest route to the relatively positively charged Earth’s surface.

The new records

• The new records for “megaflashes”, verified with new satellite lightning imagery technology, more than double the previous values measured in the United States of America and France.
• The findings were published by the American Geophysical Union’s Geophysical Research Letters ahead of International Lightning Safety Day on 28 June.
• WMO’s Committee on Weather and Climate Extremes, found that:
  • World’s greatest extent for a single lightning flash is now 440.6 miles. The world’s greatest extent for a single lightning flash is a single flash that covered a horizontal distance of 709 ± 8 km (440.6 ± 5 mi) across parts of southern Brazil on 31 October 2018.   
  • The greatest duration for a single lightning flash is 16.73 seconds from a flash that developed continuously over northern Argentina on 4 March 2019.
    
    

Lightning around the world

• At any given time, there are about 2,000 thunderstorms raging across the globe and 100 lightning strikes to earth per second.
• Lightning is more common at higher altitudes and near the equator.
• Brazil recorded a lightning strike that travelled a distance of 709 kilometres, while Argentina recorded a strike that lasted for 16.73 seconds.

Lightning strikes in India

• Lightning strikes during the June-September annual monsoon are fairly common in India.
• As a whole, India sees 2,000-2,500 lightning deaths every year on average. Lightning is the biggest contributor to accidental deaths due to natural causes.
• More than 2,300 people were killed by lightning in India in 2018, according to the National Crime Records Bureau and at least 2,000 people have died in lightning strikes every year since 2005.
• One of the reasons cited for the high number of deaths is the large number of people working outdoors in India compared to other parts of the world, which makes them more vulnerable.

Tracking of lightning events in India

• Lightning remains among the least studied atmospheric phenomena in the country. Just one group of scientists, at the Indian Institute of Tropical Management (IITM) in Pune, works full-time on thunderstorms and lightning.
• Occurrences of lightning are not tracked in India, and there is simply not enough data for scientists to work with.
• Often, safety measures and precautions against lightning strikes do not receive as much publicity as other natural disasters such as earthquakes.

Monitoring of lightning across the world

• Historically, lightning has been monitored on ground-based networks, which are limited in coverage in much of the world.
• Lightning monitoring changed drastically in 2016 and 2017 when GOES-16 was launched into space and became operational and offered a new tool, the Global Lightning Mapper (or GLM).
  • The GLM monitors flashes of light emitted by lightning day and night and over much of the Western Hemisphere.
  • It detects flashes from both cloud-to-cloud lightning and cloud-to-ground flashes.

Listing of weather extremes

• The WMO Archive of Weather and Climate Extremes maintains official records of the world, hemispheric and regional extreme records associated with a number of specific types of weather.
• Presently, the Archive lists extremes for temperature, pressure, rainfall, hail, wind, and lightning as well as two specific types of storms, tornadoes and tropical cyclones. 

Conclusion

Lightning is a major hazard that claims many lives every year. The findings highlight important public lightning safety concerns for electrified clouds where flashes can travel extremely large distances