Weather

Why do some supercells spawn tornadoes and others do not? Study hopes to find out.

For all they’ve learned about tornadoes in recent years, weather researchers are still baffled by one basic question:

Why do some thunderstorms form tornadoes and others don’t?

“That last two kilometers and last 20 seconds” before a tornado forms, “it’s really still pretty perplexing exactly what goes on,” said Erik Rasmusssen, a research scientist for the Cooperative Institute for Mesoscale Meteorological Studies in Norman, Okla.

Rasmussen is part of TORUS, a collaborative research project being conducted this spring and next by more than 50 scientists and students.

Funded with $2.4 million from the National Science Foundation and the National Oceanic and Atmospheric Administration, the study’s goal is to get a closer look than ever at supercell thunderstorms – the beasts that typically produce the strongest tornadoes.

Day after day for nearly two full weeks now, TORUS researchers have been gathering data from storms during one of the most active stretches for tornadoes in years. They’re targeting the environment close to the ground in the moments before tornadoes form.

“We were lucky in that regard,” said Adam Houston, professor of atmospheric science at the University of Nebraska in Lincoln and one of the leaders of the project. “We’re taking advantage of the opportunities that are placed in front of us. We’ve been executing our mission objectives well.”

TORUS, or Targeted Observations by Radars and UAS of Supercells, is using three drones, three mobile radars, eight mobile data gathering stations, a mobile surveying system that uses lasers to measure distance, three mobile sounding systems and one of NOAA’s P3 aircraft known as a hurricane hunter.

The drones, radars and data stations target storms in tandem to gather information from different elevations and directions. The hurricane hunter is using Salina’s airport as its operating base during the field study because of its centralized location and lengthy runways.

“It’s an honor and a privilege” for Salina to serve as an operations base for the study, Salina Airport Authority Executive Director Tim Rogers said.

NOAA has used Salina’s airport as an operations base for a number of previous field studies, Rogers said.

“It’s still very special” to be involved “because of the significance of the work and the uniqueness of the work,” he said.

The study is providing a tangible boost to Salina as well. The project is estimated to provide an economic impact of more than $750,000 this spring, Rogers said.

The 2019 field study began on May 15 and will conclude on June 16. The project covers 367,000 square miles, stretching from North Dakota to Texas and from Iowa to Wyoming and Colorado.

Airplane enthusiasts can track the hurricane hunter, nicknamed Kermit, on the Flight Aware website using Kermit’s tail number, N42RF.

Through 10 days of operations, TORUS teams have targeted 12 storms – six of which developed tornadoes. But even supercells that didn’t generate tornadoes are important for the research, Rasmussen and Houston say, because they can provide important clues about what is missing.

Using the armada of equipment, TORUS teams have gathered hundreds of thousands of measurements, including wind observations, temperatures, barometric pressure readings and humidity levels in different sectors of the storms.

“Our science focus has really narrowed down,” Rasmussen said. “We’re looking more at problems we know we can get the data to answer instead of casting a wider net.”

Researchers have been able to gather the data they wanted, Rasmussen said, though it will take time to figure out if the readings provide the clues they need.

“If we can connect those pieces, we can go a whole lot further” in figuring out “which of the storms have the higher and lower probability of tornado production,” Rasmussen said.

By understanding the mechanics of what triggers tornadoes, he said, “we’ll really improve the forecast.”

Previous field studies of tornadoes such as VORTEX and VORTEX2 have generated as many questions as they have provided answers, and researchers say TORUS may well do the same by the time it wraps up in 2020.

But they’re feeling pretty good about what they’ve been able to accomplish so far.

“I think we’re going to have some pretty strong feelings for why some” storms “are yes and some are no,” Rasmussen said.

Past research projects have sometimes struggled to find storms from which to gather data. That hasn’t been a problem this spring.

“We’ve been going really hard the last week and a half to two weeks,” Houston said. “We’re all fortunate that the pattern was set up to collect the data we need.”

In fact, the research group is grateful a lull has arrived in the active weather pattern as May drew to a close.

“It’s time for a break,” Houston said. “Our people have needed it and our equipment has needed it.”

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