San Diego Scientists Track The Region’s Biggest Rainmakers
Wednesday, October 28, 2020
Photo by Erik Anderson
San Diego researchers are getting a better understanding of the storm systems that bring the region most of its rain and they are getting that information the old fashion way — from weather balloons.
Last March, gray rain-filled skies seemed to dip into the ocean as a storm moved across the region.
It was a busy 24 hours for Chad Hecht, Allison Michaelis, and Brian Kawzenuk.
The Scripps Institution of Oceanography researchers shared balloon launching duty as a swift, wet storm river passed through the region.
Every three hours the team pulled out a package about the size of a sandwich and unwrapped a balloon with a small instrument attached.
“We put it on the spigot and are filling it up with helium,” Hecht said.
Once gas filled the balloon, the team tied off the end and secured instruments that recorded temperature, pressure and relative humidity, among other things. Once released, the balloon rushed toward the clouds, growing as the air pressure outside of the balloon dropped.
At some point, the pressure inside to balloon cannot be contained and it pops.
“Some of our recent launches overnight got up to about 23,000 meters,” Michaelis said. “And so we’re gathering temperature data, moisture data, winds data, direction, and wind speeds all the way.”
Gathering the data is important because these storm systems have an outsized influence on Southern California weather.
“An atmospheric river is supercharged with a lot of water vapor and it has a lot of wind at low altitude to push that water vapor along,” said Marty Ralph, the founder of the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography. “So it’s really a river in the sky. A river of water vapor.”
That airborne river can bring everything from a steady beneficial rain that can ease the risk of wildfires to damaging rainfall strong enough to cause floods.
But researchers don’t yet know a lot about the storm systems — AR’s as researchers call them. And that is why the weather balloons are so important.
“It turns out the core of the AR is fairly narrow horizontally and it’s hard to get a measurement right in the right spot,” Ralph said. “So we fly airplanes through them offshore to try to sample that, but we also launch weather balloons occasionally, and quite often at the coast to measure that as well.”
The ongoing research will allow scientists to better understand these storm systems so they can predict when they happen, forecasters will be able to say how intense the storms will be and weather watchers will be able to gauge the impact on land.
The launches last spring at the Scripps Institution of Oceanography Pier are already paying dividends.
“We just collect observations,” Hecht said. “That gives us information about these systems, both meteorologically and the physical processes that are occurring that could lead to extreme precipitation in Southern California.”
An analysis found current weather models fell short. Especially when researchers looked at something they call "integrated vapor transport."
“Which is essential, how much moisture is moving in the atmosphere, in what direction and how strong,” Hecht said. “And it was forecasting about 300 integrated vapor trail. We were able to observe about 600, almost twice as much as what was being forecast.”
Current storm prediction models also missed a bit on the exact location of the river and that is important because forecasters want to predict exactly where the narrow bands of rain will hit land.
“Because we had the observations we were able to see that the models were actually a little incorrect with the placement of the AR and it actually was further north than what was expected,” said Brian Kawzenuk, an application programmer at the center.
Researchers have balloon launching stations in San Diego, Orange County, near Sacramento, and a couple of spots north of San Francisco. That helps them track a lot of storms.
Meanwhile, the Center for Western Weather and Water Extremes is working with water managers around the state.
Researchers hope better storm prediction models will make it easier to manage California’s scarce water supplies.
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