THe said the storm raged through California for more than five days. As the powerful atmospheric river made landfall, ferocious winds and torrential rain tore trees from their roots, turned roads into rivers, and washed mud into houses.
The storm brought chaos as well as opportunity. Scientists were preparing to deploy instruments to measure these atmospheric rivers, both on the ground and in flight. They released the tools from airplanes equipped with small parachutes, or attached them to balloons and launched them from the ground directly into the path of the storm.
These small but powerful devices provide critical intelligence that helps improve weather forecasting as the climate crisis makes already powerful storms even more dangerous.
Atmospheric rivers have long been a key feature of weather systems across the western United States and are essential to replenishing the state's reservoirs and snowpack. But the powerful system that transports water across the Pacific Ocean, filled with water comparable to, and often many times more than, the flow of the Mississippi River, often causes some of the most destructive flooding. .
Warming oceans are making storms more intense, more dangerous and more damaging. This week's storms killed nine people, caused an estimated $11 billion in damage and economic losses, and dumped half of Los Angeles' annual rainfall in just a few days.
Scientists are now racing to better understand these systems before they deteriorate. This effort has significantly improved the accuracy of weather forecasts, giving water managers more time to plan and allowing communities to prepare warnings sooner, long before the clouds darken overhead. But there is much more to learn about these systems, especially as the dangers posed by them increase.
Research on these airborne water vapor plumes drawn from the tropical Pacific Ocean has increased dramatically in the 30 years since they were given the name “atmospheric rivers.” But predictions of where a storm will make landfall can still be off by hundreds of miles, making it difficult to predict how a particular storm will develop.
Scientists are working to understand the multilayered and complex conversations that occur between the ocean, atmosphere, and land, and are gaining stronger insight into when, where, and how storms form. I hope.
“The more we learn, the more we realize we need more data on this issue,” said Mike Sonnewald, leader of the Computational Climate and Oceans Group at the University of California, Davis.
Sonnewald, an oceanographer who uses computer science to gain insights into climate and long-term weather forecasting, added that recent advances in the satellite era are helping to paint a complete picture of ocean-atmosphere interactions. . Figuratively speaking, that photo still has too few pixels.
“We don't necessarily have enough resolution to be able to model specific things,” she adds, adding that the dynamic nature of the ocean and how easily small changes can lead to large changes in models makes it difficult to predict. It was explained that this would cause the above problem.
“The climate is changing and the planet is getting hotter. It's no secret. It's the details that are difficult to discern,” Sonnewald said. As the atmosphere warms, it could hold on to exponentially more water vapor, and rising sea surface temperatures will cause it to evaporate faster, making it easier for scientists to predict how the situation will worsen. can. Knowing when and where is even more difficult.
Inside the storm system
Even days before the storm hit, it was clear that it would have a big impact. As the turn approached, authorities had enough information to prepare resources and warn residents.
Alex Lammers, a warning coordinating meteorologist at the Weather Prediction Center, said the global models scientists rely on to make forecasts “sniff out the possibility of an impactful storm at least several days in advance.” He said he is very good at it, but doesn't know the details yet. Shape until the storm is fairly close.
“The details are really important: the exact location where it intersects the coast, which mountain ranges it’s impacting, and the angle at which the wind is impacting the mountains and slope areas,” Lammers said.
There are limits to how satellites can fill the information gap over the ocean. “The Pacific Ocean is so vast that there aren't a lot of actual weather observations,” he says.
That's why a team of scientists led by Martin Ralph, founding director of the Western Weather and Extreme Waters Center at Scripps Institution of Oceanography, set to work. Measure Directly from within the storm system itself.
Since 2016, the Atmospheric River Reconnaissance Program (AR Reconnaissance) has relied on the U.S. Air Force's “Hurricane Hunter” aircraft, which drop clusters of small instruments known as dropsondes, which fall through clouds to the ocean below. The results of the investigation can be communicated at the time of the investigation. .
Each dropsonde is attached to a small parachute and floats through the clouds and out to sea. Sailing takes approximately 20 minutes. All the while, important observations are fed back to scientists onboard. Temperature, pressure, water vapor and wind speed are all collected by dropsondes, like “his MRI of atmospheric rivers,” according to Ralph, allowing researchers to see inside the system without relying on satellite images. That's what it means.
During a series of strong atmospheric river storms that hit California in 2023, dropsondes helped advance some heavy rain forecasts by about 12%. The researchers believe this is an achievement that would have taken another eight years using traditional data collection methods.
“If we make mistakes in modeling the strength, location, structure, and amount of water in atmospheric rivers, those errors will create errors in long-term predictions into the future,” Ralph said. , explains the importance of going to specific locations and measuring atmospheric rivers.
In addition to parachuted dropsondes, traditional weather balloons called radiosondes, which are released from the ground during storms, help complete the picture. “These are very different approaches, but both are needed to achieve the most effective predictive systems,” says Ralph.
The researchers are also using new technologies, including a technique called airborne radio occultation (ARO), invented by Scripps geophysicist and atmospheric scientist Jennifer Haas. Dropsondes take measurements while falling vertically below the plane, while ARO takes measurements horizontally using sensors mounted on the side of the plane. By measuring how much GPS signals refract as they travel through the atmosphere, properties such as moisture and temperature can be inferred, helping scientists paint a more complete picture of incoming storms.
The first ARO-equipped aircraft was deployed this winter and could collect data at distances up to 186 miles (300 km) from the plane.
Mitigating the worst disasters
California and other parts of the arid western United States are at increased risk of flooding, and more accurate information is essential to mitigating the worst disasters.
Alex Hall, an atmospheric physicist and climate scientist at the University of California, Los Angeles, said: “Given the degree of warming observed to date, large-scale precipitation events are likely to result in greenhouse gases being added to the atmosphere. “It should be about 10% more intense than before.” .
“The scary thing is that if we look into the future to the point where the warming is twice as much as it is today, we're going to see events that are 20% more intense, and we're going to see a whole new class of events that don't even exist today.”
For Ralph, this reality is a call to arms.
“As these storms evolve and change over time, the development of AR reconnaissance and related tools to measure and predict atmospheric rivers will be able to keep up,” he said. “This is really a climate mitigation strategy that allows humans to better adapt to what's going on.”