Storm-hunting planes chase atmospheric rivers through the sky from Japan to the US, revealing new insights into these powerful storms and how we can keep ourselves safe.

It was an early morning in February, and Capt Nate Wordal, a storm-hunting US Air Force pilot, was flying out of Yokota Air Base west of Tokyo. After fighting some turbulence coming off Mount Fuji, he was headed for the vast, blue expanse of the Pacific Ocean. His destination: a type of storm known as an atmospheric river, which was developing off the coast of Japan.

Atmospheric rivers are invisible ribbons of water vapour in the sky. The ones Capt Wordal was hunting form in the Pacific Ocean then travel eastwards to the US West Coast. When they hit the coast and flow up the mountains, the vapour cools, turns into rain or snow and is dumped on the ground – where it can bring devastating floods and avalanches. But the "sky rivers" also bring benefits, and are vital for preventing droughts: in California, they contribute up to 50% of annual rain and snow in just a few days each year. They occur in winter – which for storm-chasing pilots like Capt Wordal, adds another job after the summer hurricane season.

"Our main mission during the year is hurricane hunting," says Capt Wordal, a hurricane hunter with the Air Force 53rd Weather Reconnaissance Squadron. He usually spends the months between May and November flying through hurricanes and dropping weather instruments that capture real-time data for the National Hurricane Center. "And then our next season that we've started in the last few years is this atmospheric river mission," he adds, where the flights gather data on those storms, typically between November and March.

This year, for the first time, some of the flights started in Japan, in addition to flights out of Hawaii and the US West Coast, to measure the storms early on in their journey and create more accurate forecasts.

Generally speaking, "our weather is moving west to east around the northern hemisphere, so the more accurate information you have about a storm further [west], the more you can understand how it's going to evolve," including how much rain or snow it will bring once it makes landfall, says Anna Wilson, an extreme weather specialist. Wilson is the field research manager for the Center for Western Weather and Water Extremes at Scripps Institution of Oceanography at the University of California, San Diego – which is is one of the partners of the mission, along with the National Oceanic and Atmospheric Administration (Noaa).

The flights, known as the Atmospheric River Reconnaissance campaign (or AR Recon for short), were started almost 10 years ago by Scripps, Noaa and the Air Force. The missions have grown in scope and reach since then, as atmospheric rivers and their impact have been increasingly in the spotlight.

In the western US, atmospheric rivers are the main cause of flood damage, causing more than $1bn (£753m) a year in such damage. They are becoming bigger, and the strongest ones are becoming more frequent, due to climate change, as warmer air holds more moisture. But people's ability to forecast, prepare for, and cope with these storms and the floods they bring, is also advancing – helped by data from the flights.

"We fly to the [atmospheric river], we cross it multiple times if we can. We really target the [atmospheric river] itself as well as the weather conditions........

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