STOCKVILLE, Neb. — Penn State professors Paul Markowski and Yvette Richardson have a pretty unusual job. They launch weather balloons into supercell thunderstorms.
These rotating storms are what most commonly produce tornadoes and the data these scientists collect could improve their forecasts.
“We’re trying to go where traditional instruments haven’t gone before,” said Markowski. “This is something new.”
The team aims to launch miniature weather balloons about 12 to 16 inches in diameter into the air at the periphery of the storm. Attached to each balloon is a probe that measures temperature, dew point and relative humidity. Markowski hopes his team can use the data to re-create the near-surface temperature field of the environment surrounding and within the storm.
“The horizontal temperature gradient in storms has a huge role in determining buoyancy,” explained Markowski. Buoyancy describes the air’s affinity to rise. Hot air balloons are positively buoyant. But if suddenly all the air inside were chilled, the balloon would sink. The same premise applies to pockets of air in the atmosphere. If air is buoyant and rising, a tornado is more likely to form.
“Buoyancy can in turn influence vorticity,” said Markowski. Vorticity describes the amount of horizontal rotational energy present at different levels of the atmosphere. It’s one of many ingredients that interact to ultimately contribute to tornadogenesis — tornado formation.
“We’re not launching balloons into tornadoes themselves,” said Yvette Richardson. “We’re sampling regions that the inflow air will pass through en route to the tornado.”
Launching balloons may seem like a straightforward process, but designing a balloon-carried apparatus that can transmit data in real time is an entirely different challenge.
“It used to be that we’d need a different frequency and receiver for each probe we launched,” said Markowski. “When we’re launching up to two balloons per minute, that’s just not feasible.”
In recent years, however, it’s been possible to partition “time slots” on an individual frequency.
It’s sort of like a conference call. If 50 people were in the same phone conversation talking at once, no information would get through. But if the time was divided up and each person took a turn to talk, all the information would get through.
That technology has made an endeavor like Markowski’s possible. But it comes with a tradeoff. “The more probes we launch, the more things we have to keep track of, and the less resolution we can get time-wise.”
The team also had to design a setup in which the balloons would rise slowly. The faster they move, the quicker they pass through a given layer, and less data points can be collected. “We have to get it just right,” said Markowski. “The balloons have to actually take off and rise, but not too fast. And if even a few raindrops — the weight of a penny or less — can make a balloon … stop, or even start to descend.”
“Each probe we launch has a cost,” said Markowski. “Radar you can just scan. It’s expendable. But we have to be careful to only launch balloons into worthwhile storms.”
Markowski’s project has been a long time in the making. “Some people have asked why we’re not using drones. The Federal Aviation Administration doesn’t allow people to fly drones into places without visual contact,” he explained. “Besides, drones aren’t really disposable.”
This year, the team sampled a number of storms, taking advantage of the severe season to collect data. “We were out there for 11 days this year, and got to deploy balloons on multiple strong supercells,” said Richardson. “We went during 2017, but it was a much quieter season.” Markowski says the project is still in the era of “beta testing” to an extent, but estimates they’ve launched about 220 probes since the start.
Markowski hopes the team’s 3D temperature mapping may help make progress on one of the biggest weaknesses of storm modeling: precipitation.
“We can run storm simulations and computer models, but all of them make the same assumptions on how to handle precipitation.” When computers make guesses about temperature, they’re also making conjectures about the distribution of water droplet sizes. “We know there’s a finite amount of water that enters the storm. But what that water ends up as — whether it be big hailstones or tiny droplets of mist — is extremely important in terms of the physics.” Better understanding subtle temperature variations could make bountiful progress in this area.
