The lightning season in the Southeastern U.S. is almost finished for this year, but the peak season for the most powerful strokes of lightning won’t begin until November, according to a newly published global survey of these rare events.

A ÌìÃÀÓ°ÊÓ´«Ã½ maps the location and timing of “superbolts” — bolts that release electrical energy of more than 1 million joules, or a thousand times more energy than the average lightning bolt, in the in which lightning is most active. Results show that superbolts tend to hit the Earth in a fundamentally different pattern from regular lightning, for reasons that are not yet fully understood.

The study was published Sept. 9 in the , a journal of the American Geophysical Union.

“It’s very unexpected and unusual where and when the very big strokes occur,” said lead author , a UW professor of Earth and space sciences who has been tracking lightning for almost two decades.

Holzworth manages the , a UW-managed research consortium that operates about 100 lightning detection stations around the world, from Antarctica to northern Finland. By seeing precisely when lightning reaches three or more different stations, the network can compare the readings to determine a lightning bolt’s size and location.

The network has operated since the early 2000s. For the new study, the researchers looked at 2 billion lightning strokes recorded between 2010 and 2018. Some 8,000 events — one in 250,000 strokes, or less than a thousandth of a percent — were confirmed superbolts.

“Until the last couple of years, we didn’t have enough data to do this kind of study,” Holzworth said.

The authors compared their network’s data against lightning observations from the Maryland-based company Earth Networks and from the New Zealand MetService.

The new paper shows that superbolts are most common in the Mediterranean Sea, the northeast Atlantic and over the Andes, with lesser hotspots east of Japan, in the tropical oceans and off the tip of South Africa. Unlike regular lightning, the superbolts tend to strike over water.

“Ninety percent of lightning strikes occur over land,” Holzworth said. “But superbolts happen mostly over the water going right up to the coast. In fact, in the northeast Atlantic Ocean you can see Spain and England’s coasts nicely outlined in the maps of superbolt distribution.”

“The average stroke energy over water is greater than the average stroke energy over land — we knew that,” Holzworth said. “But that’s for the typical energy levels. We were not expecting this dramatic difference.”

The time of year for superbolts also doesn’t follow the rules for typical lightning. Regular lightning hits in the summertime — the three major so-called “lightning chimneys” for regular bolts coincide with summer thunderstorms over the Americas, sub-Saharan Africa and Southeast Asia. But superbolts, which are more common in the Northern Hemisphere, strike both hemispheres between the months of November and February.

The reason for the pattern is still mysterious. Some years have many more superbolts than others: late 2013 was an all-time high, and late 2014 was the next highest, with other years having far fewer events.

“We think it could be related to sunspots or cosmic rays, but we’re leaving that as stimulation for future research,” Holzworth said. “For now, we are showing that this previously unknown pattern exists.”

Co-authors are research associate professor and senior research scientist at the UW; and and at the University of Otago in New Zealand. The research was funded by the UW.

For more information, contact Holzworth at bobholz@uw.edu or 206-685-7410.

This scientific mission, led and funded by the U.S. Naval Research Laboratory, will simultaneously create and observe “dusty plasmas” in Earth’s outer atmosphere. These hot, charged clouds of ions, electrons and dust form and dissipate naturally when swift-moving objects move through the atmosphere — from a satellite launching into orbit to a meteorite burning up in the atmosphere. Dusty plasmas are thought to be a common source of interference for radar and radio communications.

“From a practical standpoint, normal atmospheric dynamics can get completely disrupted for a period of time,” said UW professor of Earth and space sciences , who is working on this project along with his departmental colleague professor .

Dusty plasmas are complex, transient mixtures of gas and dust that have been difficult to observe and characterize when they arise naturally. The mission of the Charged Aerosol Release Experiment II — or CAREII — is to use rocket engines to generate a dusty plasma and simultaneously measure its characteristics using sensors on the rocket itself. UW researchers designed and constructed instruments in the rocket that will measure the dusty plasma’s electrical field. Collaborators with NASA provided launch and support services, while scientists at the , under the project lead investigator Paul Bernhardt, provided additional instruments and the CRV7 rockets that will create the dusty plasma. The U.S. Department of Defense Space Test Program provided payload integration and launch services.

Plasmas are gases in a superheated and charged state. Scientists can predict the behavior of plasmas with a known composition based on the types of gases and other particles present. But dusty plasmas are too intricate to predict using current theories of plasma physics, said Holzworth.

“Most plasmas in the atmosphere are actually ‘dusty’ in that they have extra stuff in them like dust and aerosols,” said Holzworth. “That’s a problem because our descriptions of plasmas and how they behave really don’t apply to much of anything that we study in the real world. So as we learn more we’re hoping we can improve our models and understand how dusty plasmas work in the atmosphere.”

The CAREII mission follows up on the success of in 2009, which used a rocket launched from NASA’s Wallops Flight Facility to create a dusty plasma in the skies above Virginia, which scientists observed using ground-based equipment.

The CAREII rocket will launch from the , a rocket launch facility above the Arctic Circle near Andenes, Norway.

“You want the dusty plasma illuminated but you want it dark on the ground,” said Holzworth. “That’s a narrow window that’s typically longer at higher latitudes — about a half hour every day.”

The CAREII mission has a two-week window starting on Sept. 7 to launch the rocket. The team will wait for ideal visibility and atmospheric conditions to send the rocket up into the atmosphere, McCarthy said.

After it ascends over 160 miles into the atmosphere, the rocket will begin to fall back to Earth. At about 145 miles above the Norwegian Sea, the forward section of the rocket — which contains most of the scientific instruments — will detach and aim its instruments toward the aft section. The aft section will then simultaneously fire 37 small CRV7 rocket engines, designed by Bristol Aerospace in Canada, creating a dusty plasma of known gas, ion and dust composition that will envelop the forward section of the rocket. Probes and sensors in the forward section — including the UW’s electric field instruments — will soak up information about the dusty plasma. Radar and stations on the ground and a nearby plane packed with cameras and sensors will also track and measure the artificial plasma.

“From start to finish, it will take 10 minutes,” McCarthy said.

The electric field instruments that Holzworth and McCarthy designed reside on four mechanical arms — or booms — that will be deployed outward from the rocket once the forward and aft sections separate. The booms keep the eight electric field sensors 6 to 10 feet apart so they can gather accurate information about electric fields within the dusty plasma.

“The sensors are separated far apart to get them away from the rocket body, which perturbs the plasma you’re trying to measure,” said McCarthy. “Also, we’re trying to measure small electric fields, so if we have things farther apart we can get a better signal.”

Holzworth and McCarthy hope that this project will give them a glimpse at how complex plasmas truly behave. The data they and their colleagues collect could illuminate how dusty plasmas in the atmosphere disrupt radio-based communications and tracking systems. But on a more fundamental level, CAREII could reveal basic characteristics about a common phenomenon.

“We don’t know what we’re going to see,” said Holzworth. “It’s very much an experiment of investigation.”

Holzworth and McCarthy have already started thinking of the types of sensors and equipment they would like on a future dusty plasma mission, should there be funding to get a CAREIII endeavor off the ground.

Funding for the CAREII project comes from the U.S. Naval Research Laboratory and the Department of Defense Space Test Program.

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For more information, contact Holzworth at 206-685-7410 or bobholz@uw.edu or McCarthy, who is currently in Norway for the launch, at mccarthy@u.washington.edu.

Update: the CAREII rocket was launched successfully on Sept. 16, .