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Don’t Go Chasing Waterfalls: Professor Chases Thunderstorms Instead

When Deanna Hence, Assistant Professor of Atmospheric Sciences at the University of Illinois at Urbana-Champaign went to Argentina’s Malbec-rich Mendoza region to study severe thunderstorms, she didn’t have to wait long for the perfect storm. One moved into San Rafael, one of the cities she was staying in, and dumped hail the size of golf balls over the city.

Most people would be petrified to encounter such a storm, but not Hence. In fact, her primary reason for traveling there was to study hail’s formation processes. The Córdoba region of west central Argentina (between the Sierras de Córdoba and the Andes foothills) hosts some of the strongest thunderstorms and is one of the biggest producers of hail in the world. As part of an international field campaign called RELAMPAGO, which stands for Remote sensing of Electrification, Lighting and Mesoscale/microscale Process with Adaptive Ground Observations, Hence and 26 other scientists wanted to find out why this particular region created such storms.

Extreme weather was abundant during the project. Early on, one hailstorm damaged an expensive, new truck-mounted radar. The hailstones knocked two-inch dents into the radar’s dish.

On the trip — sponsored by the U.S. National Science Foundation (NSF), National Oceanographic and Atmospheric Administration (NOAA), NASA, and others — teams took Doppler radars, weather balloons, weather observation towers, and other instrumentation to study the thunderstorms they were following.

Hence was part of the mobile sounding team that launched radiosondes — instruments carried by balloons that use radio transmitters to send information back on temperature, pressure, humidity — and used GPS technology to help measure the wind. The data they collected will be archived at the National Center of Atmospheric Research. This information is exactly what Hence and her colleagues needed to help explain why that region is so prone to severe thunderstorms.

Once a decision to deploy was made, the mission scientists made an operational plan they distributed to the mobile teams — which included hail measurement teams from Australia, New Zealand and the University of Córdoba — and from there, the teams went out into the field with their instruments.   

Deanna Hence
Deanna Hence. Credit: L. Brian Stauffer.

“I drove all over the region in a little pickup truck with a helium tank and a bunch of balloons and a bunch of radiosondes (telemetry instruments)…sitting in a place for several hours, launching a balloon every hour,” Hence, a AAAS Member, explains.

Aside from fieldwork, Hence also served as the science director and worked in the operations center. She used the data collected by the central operations center to direct other teams.

“When we have a mission going in real time, then we can both look at how the data’s coming in and the quality of it,” Hence says. “And we’re also keeping an eye on the weather to make sure the team is safe.”

Sometimes she had to tell teams to get out of the way — that part of Argentina frequently floods. The areas they sampled were fine, but a couple of times, a storm rolled through, flooding Villa Carlos Paz, another town where the teams were living.

The groups completed 19 missions overall, each with separate goals. For example, one looked at how individual thunderstorms grow into larger systems. Another focused on severe weather hazards like wind, hail, tornadoes and more. The focus determined sampling strategies, where to put the instruments, what sort of radar scan strategies to use, and the like.

Time of the day also mattered. If they were looking at wind storm initiation, it was best to go out early in the day. But if scientists were examining upscale growth, that tends to happen overnight.

“We can’t have people out with these instruments 24 hours a day, so there’s a lot of tough decisions about do we deploy early in the day or overnight, or early in the morning to focus on these other objectives.’” Hence says. “There’s a lot of decisions that have to be made around that.”

Hence studies hazardous weather tropical cyclones and orographic precipitation because they directly impact human life. Not only can they injure and kill people, but they can also be very destructive in terms of damage to property and infrastructure.

“The societal importance to better understanding these weather systems is quite large because of the direct threat,” Hence says.

By studying hail, Hence is following a childhood passion. Growing up in north Texas in the Dallas-Fort Worth area, she was surrounded by severe weather, which spurred her interest in the topic. Her mother turned the news on every morning and Hence couldn’t take her eyes off the meteorologists’ colorful presentations of the weather.

“I just loved watching the radar,” Hence says. “They would show how storms were moving across the state, and I really, really loved that.” 

Hence has a particular interest in hail because of all the injuries and property damage it can cause. For example, it’s known for flattening crops. In the enormous Mendoza province of Argentina, the largest wine region in the country and main producer of Malbec grapes worldwide, she noticed nets were strung across entire crops to catch the hail stones before they hit and bruised the grapes. And in the Rocky Mountains of the U.S., the front range of the mountains are known for getting hail, which can be a large source of insurance claims. Other trips have taken her to the Maldives, Florida, western Virginia, southern Illinois, and Washington State.

In the future, she’s hoping to go on a campaign next spring to Japan and Taiwan to study orographic precipitation, which is rain, snow and other precipitation made when moist air is lifted as it passes over a mountain range. She would research how thunderstorms and tropical cyclones interact with the mountains there.