It’s a little after 6:30 p.m. when Aidan Sesnic calls a huddle for members of the CU Boulder TORUS team on the side of a lonely dirt road in rural Oklahoma. This particular safety briefing would be standard, if not for the large black- and green-tinged supercell thunderstorm crawling across the soft, rippling plains behind him.
Sesnic is bathed in warm light from the rapidly setting sun as he calmly and quickly lists the weather conditions and possible issues, such as powerlines near the landing space, from a checklist. The aerospace engineering sophomore’s group is one of three nearby, all preparing to launch unmanned aircraft to gather data about the storm.
Together, these groups are taking part in TORUS—the largest and most ambitious drone-based investigation of severe thunderstorms ever. The goal is to learn more how supercell thunderstorms form tornadoes and eventually to increase tornado warning times. Faculty, staff and students like Sesnic from the College of Engineering and Applied Science are at the heart of it all.
When the briefing ends, Sesnic pilots a drone up and into the area near the storm to collect wind speed, air pressure, precise GPS location data, and other information about the storm that ground-based research teams simply cannot get. The process is made more impressive by the speed with which it occurs. Depending on other teams’ success that evening–and the storm itself–Sesnic’s group can redeploy to get more data or quickly move out of danger should the storm shift. That level of mobility, flexibility and coordination is unprecedented for a CU team that has become quite experienced in this potentially life-saving research area over the last 25 years.
Meet the RAAVEN
Project TORUS–or Targeted Observation by Radars and UAS of Supercells–is a two-year partnership between CU Boulder, the University of Nebraska-Lincoln (which is leading the work), Texas Tech University, the University of Oklahoma and the National Severe Storms Laboratory. Funding comes from the National Science Foundation and the National Oceanic and Atmospheric Administration. Support also comes from the CU Grand Challenge and the Integrated Remote and In Situ Sensing initiative, or IRISS. The goal is to collect data to improve the conceptual model of supercell thunderstorms, the parent storms of the most destructive tornadoes, to help with future forecasting and warning.
In 2010, CU Boulder engineers were the first in the world to deploy an unmanned aircraft system to collect data from supercell thunderstorms. The lessons learned from constructing and using that aircraft and the following versions informed the design of the new RAAVEN aircraft.
Piloted by students and staff, the drones were catapulted from the roof of an SUV, or a launcher placed on the ground, into the storms in spring 2019. In all, the CU team deployed up to three aircraft simultaneously, totaling over 40 hours of air time on 51 flights, including seven tornado-producing storms.
RAAVEN stands for Robust Autonomous Aerial Vehicle – Endurant and Nimble. Built from lightweight yet high-strength foam from RiteWing RC, the drones also include an avionics system and many other aspects custom-built by the IRISS team. That includes the car launch system, which can launch a 15-pound aircraft up to 50 mph in less than a second.
The drones are modular in design, meaning parts from one can be used to repair another. The result is fewer down days for large repairs and easier fixes in the field. They also don’t use landing gear, removing a breakable part and making it easy to land the aircraft virtually anywhere.
“The way we launch these and their durability have made us much nimbler in responding and re-deploying than we have been in the past,” said CU IRISS Engineering Manager Steve Borenstein. “I don’t think we could have designed these to work as well as they have during this project without the time in the field we have had–experiencing the conditions, making repairs and learning what was needed to get these up and get the data back.”
Aerospace engineering senior Danny Liebert pilots one of the drones for the team and said he loves how rugged it is compared to the previous “TTwistor” model.
“The TTwistor drone we used was great but just not as durable. These new aircraft are awesome. They take it like a champ out there,” he said.
IRISS Director and CU Project Co-Leader Brian Argrow said the drones have exceeded expectations for toughness and flexibility, but that isn’t the most impressive aspect of the aircraft in his mind.
“The work Steve has done with data flow and communications management on these is just as important as the airplane itself,” he said. “The things he has refined have enabled us to deploy three teams simultaneously, connected with each other and integrated with meteorologists. I am as amazed by that as I am the aircraft.”
Explore the unique features of the RAAVEN unmanned aerial vehicle:
Above: Graphic design by Rochelle Zamani, words by Josh Rhoten.
Below: Professor Brian Argrow talks with IRISS Lab Manager Michael Rhodes between deployments. Photo by Josh Rhoten, CEAS
Getting the information needed to save lives
Smead Aerospace Professor Eric Frew explains the logistical challenges of the project with the wry smile of someone who has learned a great deal of patience over his years in the field on this and similar projects.
“We call it hurry up and wait,” said Frew, who is leading the CU portion of the project with Argrow. “We call it that because you really want to position yourselves and then see what the weather's doing. Then you wait until you have a good sense of things before you rush to the next stop. We are doing this with a large team all across the Great Plains, so it really is quite a logistical challenge.”
Teams conducted fieldwork from May 13 through June 16 and covered virtually all of the Central Plains including parts of Texas, Nebraska, Kansas, Oklahoma and Colorado. It was an especially busy storm season, particularly in May, with more than 200 tornadoes reported across the entire U.S. May also included a 12-day streak with at least eight reported tornadoes, smashing the previous record set in 1980 and showing how severe the season was inside and out of the TORUS operations area.
Mornings on the project start with a weather briefing about where the team might have the best chance to intercept a supercell storm. Team leaders also look at possible intercept locations for the next two days, factoring in Federal Aviation Administration restrictions, travel distance and hotel availability for the more than 50 professional and student scientists and engineers participating. From there, it’s “hurry up and wait” with storm tracking, data collection and recovery often going late into the night. It’s a grind for the team, but data collected by these drones could have tremendous value when it comes to prediction of tornado behavior. That’s because certain variables, such as humidity, cannot be accurately measured without actually touching the storm with precise instruments. Weather balloons can get some of this information, but a fixed-wing drone offers several advantages, including more control over the specific collection points.
That all plays into the team's goal of exposing how a storm's unique structure contributes to tornado formation. Understanding this aspect better would reduce the number of false-alarm tornado warnings and improve detection of the potentially lethal storms.
“Something like 95% of the most violent tornadoes come from a supercell thunderstorm, but only single-digit percentages of supercells create these tornadoes,” Frew said. “So in order to understand what about this particular storm is leading to a tornado, you need to have a lot of data where that transition does happen and a lot of data where that transition doesn't happen so you can see what's different. Ideally, half of our data comes from storms that produce tornadoes and the other half comes from those that don’t.”
Frew said he can envision a future in which drones are used as forward deployment tools for weather prediction and data collection, responding to weather models and data from other drones in real time to decide where to go next. Work on TORUS and future projects can make that a reality.
“We can see the technology advancing to a point where small towns or individuals have these drones and they release them into precursor environments to help feed into the weather forecasting system–much like the citizen scientists who report temperature and snow or water accumulations every day around the U.S.,” he said.
With another year of fieldwork in 2020 still to come, it is too early to know what the data collected so far by the TORUS team says about supercell formation.“There’s no question that we’ve taken new, novel data that’s never been collected before,” Frew said. “But we want to get a lot of data before we really look at it and try to make some conclusions. We scheduled two years because that's what we think it takes to have a really strong dataset.”
AES senior Danny Liebert : “These new aircraft are awesome. They take it like a champ out there." Rhoten, CEAS