An “atmospheric river” is a colorful term for a curved plume of moisture that travels up from the tropics a single plume can carry more water than the Mississippi River at its mouth. The atmospheric rivers are also among the most damaging weather systems around, shows the new research. The atmospheric rivers that drowned California this winter did some good they ended an epic drought in the state.
Jeff Zimmerman of the National Weather Service reports, “This has been a very active winter, atmospheric river-wise. We’ve probably had 10 or more this winter.” The norm is just a few; being a La Nina year, with cooler water in the eastern Pacific, was part of the reason for the abundance. Atmospheric rivers are famously wet. The new research done by atmospheric scientist Duane Waliser shows they’re also remarkably windy.
Waliser studied two decades of storms around the globe at mid-latitudes that are, outside the tropics. While focusing on the very windiest the top 2 percent, he found that “atmospheric rivers are typically associated with 30 and even up to 50 percent of those very extreme cases.” Atmospheric rivers were also accountable for almost that percentage of the very wettest storms, too.
But the windiness was surprising. Waliser found that winds during an atmospheric river are typical twice the speed of the average storm. He says necessity responders need to know that. “Not only do [atmospheric rivers] come with this potential for flooding hazards,” he says, “they also come with the potential for high impact winds and extremes that can produce hazardous conditions.” In fact, the atmospheric river that hit California on January 8 knocked over a famous and gigantic sequoia in a state park.
Waliser, is with NASA’s Jet Propulsion Lab in California. He says the combination of high wind and water is especially costly. Over the past two decades, for example, Europe experienced 19 storms that each did at least a billion dollars in damage. He says, “And so out of these 19 storms, we associated atmospheric rivers with 14 out of the 19.” Waliser’s research appears in the journal Nature Geoscience. He says his next project is to find out if the change in the climate will make atmospheric rivers more frequent.