A 440-mile lightning flash? ASU scientists verify it
On a map, the drive from Apache Junction to Los Angeles is about 440 miles. Now imagine a lightning bolt stretched across the same distance.
That’s the newest world record for the longest single lightning flash, which lit up the sky on Halloween in 2018 over parts of southern Brazil.
“It must have been a mind boggling event to witness,” said Randy Cerveny, an Arizona State University professor in the School of Geological Sciences and Urban Planning. He’s also the “chief rapporteur” of global records for the World Meteorological Organization, which is part of the United Nations.
Cerveny heads the organization’s Committee on Weather and Climate Extremes, which maintains official records of global, hemispheric and regional extremes across the world. Not only did he and his team recently verify the longest lightning bolt in recorded history, they also confirmed the greatest time duration for a single lightning flash, one that lasted for 16.73 seconds on March 4, 2019, over northern Argentina.
The new records for “megaflashes” more than double the previous records. Those records were 7.74 seconds for the longest duration of a single flash, which occurred over southern France in 2012, and nearly 200 miles for the longest distance traveled by a single flash, which occurred over Oklahoma in 2007.
“This is pretty significant stuff in that we’re really rewriting the definition for what is a lightning flash,” Cerveny said. “In our scientific textbooks, the formal definition is that it’s an electrical discharge that lasts less than a second.”
What they’ve learned is not just of scientific importance. For lightning, the new records reinforce the importance of the 30-30 safety rule: If the time between the lightning flash and the thunder is 30 seconds or less, go inside and then wait at least 30 minutes after the storm has passed before resuming outdoor activities.
“What we’ve found is that lightning can travel a long way from its parent thunderstorm,” Cerveny said. “So this helps verify that this rule is a good one.”
Technology helps track records
Cerveny and his recent lightning evaluation committee, which had members from the United Kingdom, Spain,
France, Brazil, China and the US, verified the records with new satellite lightning imagery technology.
The previous assessments used data collected by ground-based lightning mapping networks, which has limits. Identifying megaflashes beyond these extremes requires a lightning mapping technology with a larger observation domain.
Recent advances in space-based lightning mapping have allowed scientists to better measure flash length and duration over broader areas. Cutting edge satellites run by NOAA, along with their orbiting counterparts from Europe and China, measured the new records. The findings were published by the American Geophysical Union’s Geophysical Research Letters on June 28.
The megaflashes occurred between clouds, rather than from cloud to ground. About 80 percent of lightning strikes are cloud to cloud, while 20 percent are from cloud to ground, Cerveny said. With cloud to ground strikes, the length of the lightning flash can only be a few miles. These particular storms were about 8 to 10 miles up in the atmosphere.
Cerveny’s committee sets the standards for the entire world for how to take weather observations.
“You want temperature measured in Siberia measured in the same exact way that it’s measured in Tempe or Phoenix,” Cerveny said.
The committee maintains the official global records of hemispheric and regional extreme records associated with a number of specific types of weather. The archive lists extremes for temperature, pressure, rainfall, hail, wind and lightning as well as tornadoes and tropical cyclones. They also name hurricanes.
Records mix science and politics
In 2007, Cerveny co-authored a paper about the need to have an official list of accepted extremes: hottest, oldest, windiest. After it published, the World Meteorological Organization contacted Cerveny and asked him to head a new committee.
Since then, Cerveny has had the final word on world weather and climate extremes.
When there is a new record, or an old record becomes disputed, Cerveny puts together an international team of top scientists from around the world to analyze the data.
“We look it all over, tear it to shreds,” Cerveny said. “In one case we were looking at a temperature record in Kuwait, the third highest we’ve ever seen, and the committee had the Kuwait government send that sensor to an independent lab in Italy for outside testing to verify it.”
Once they have gone through the data and evaluated it, the committee votes and makes a recommendation to Cerveny. He then decides whether the WMO should accept it as the new record or not.
“It’s a certain responsibility,” Cerveny said. “When I first was working with this I thought the biggest problem would be science issues, but the biggest thing I have to put up with is politics.”
For example, according to United Nations guidelines, which the WMO must follow, Israel is a part of Europe. The WMO lists the country as having the hottest temperature record for Europe at 129 degrees, just one degree higher than the all-time record for Arizona, set at Lake Havasu in 1994.
“I will get emails every so often from people around the world that Israel is not a country and I shouldn’t have that listed,” Cerveny said.
For a long time, the highest wind speed ever recorded was at Mount Washington Observatory in New Hampshire at 123 miles per hour.
“A few years ago we had an automated weather station survive a cyclone off Australia and came up with a new record: 153 miles per hour,” Cerveny said. “I got some interesting messages from New Hampshire that I was taking away something they have great pride in.”
A newspaper report even proclaimed that Cerveny’s passport to the state had been revoked, Cerveny recalled with a chuckle.
“People do take this seriously,” he said. “The hottest temperature in the world is 134 degrees, which we recorded in Death Valley in 1913. And if you go to Death Valley, they have in their National Park office lots of displays saying they are the hottest place on earth. So these records are serious.”
The numbers are not only a record, though. They provide important information that helps engineers and officials make important decisions about building durable infrastructure and protecting public health.
“If we know how windy a place can be, that’s important for designing buildings,” Cerveny said. “Knowing how hot it can get is important for public health officials to know.”