During a powerful storm, a ship bounced up and down on 20-foot waves in the black of night, “out in the middle of nowhere,” said Chris Fairall, 750 miles off the coast of San Francisco in the Pacific Ocean. “A lot of people said they didn’t sleep well at breakfast the next morning.” It was the first of several storms for the 30-member crew of the Ronald H. Brown, the largest ship in the fleet of the National Oceanic and Atmospheric Administration.

Why were 18 scientists and crew, including six from Howard University, braving rolling waters on a ship in the vast ocean between California and Hawaii? They were searching for rivers in the sky, trying to unlock the mystery of how they channel water from the tropics and dump it in various types of precipitation on California’s lakes and mountains, Fairall said in an interview Friday, talking on a satellite telephone.

Atmospheric rivers, as they are called, carry enormous amounts of waters that have caused damaging floods, but predicting where they will strike can help officials avoid harm and possibly manipulate the water for more beneficial usage, particularly in a region suffering drought, such as California today. NOAA scientists have studied atmospheric rivers for more than a decade, but they had never succeeded in convincing the agency to include the Cadillac of its ship fleet to participate, said Fairall, a NOAA physicist.

For the first time, scientists on the ship will study how water in the ocean contributes to rivers carrying vast amounts of water in the sky. The CalWater project started in mid-January and will end in mid-March.

“These rivers are an important global phenomenon,” said Allen B. White, a NOAA meterologist who waits for a chance every day at an airport in Sacramento to hop in an agency jet and fly in and above the sky rivers at 45,000 feet to drop various electronic devices and other gadgets to study them. “It’s scary,” he said. “All you see out the window is fog, rain pelting the windows and it’s very bumpy.”

White also said: “They’re similar to hurricanes. They produce copious amounts of rainfall and can be a blessing in disguise.”

Or a curse. More than 40 atmospheric rivers dumped water on California in winter between 1997 and 2006, causing seven floods, NOAA said. The so-called “New Year’s Day Flood” in 1997 caused more than $1 billion in damage. Another sky river in 2006 caused more than $50 million flood damage in the Pacific Northwest. “Our role is to give the public more warning about when these atmospheric rivers will hit,” White said.

“The frequency and strength of [atmospheric rivers] in a given region over the course of a typical west-coast wet season greatly influences the fate of droughts, floods, and many key human endeavors and ecosystems,” NOAA said in an explanation of the phenomenon. Better  climate forecasts coupled with weather forecasts “can improve water management decisions,” the agency said.

For White, mornings in Sacramento start with a forecast that seeks to pinpoint where an ocean river might pop up over California. “The briefing is to see what happens with them, whether they’re bending or curving or straight, to get up there fast in a Gulfstream jet, essentially a fast-moving laboratory,” he said.

A river flowed above White’s head as he spoke during a telephone interview, but its behavior wasn’t good for California, or its eventual destination, British Columbia. It bent around a persistent blocking ridge, White said, and bypassed the state. Worse, it was acting according to script at the end of its journey. Rather than dumping snow on the Whistler ski area, it showered the famous vacation spot with too much rain.

On the ocean, Fairall’s group is task with looking at instruments on the ship that measure vapor, air pressure and wind as the river passes by. The data is transmitted to other NOAA science centers, where it is studied.

“It was pretty nasty out here last night,” Fairall said. But the crew had to stay alert, he said. “We expect an atmospheric river sometime tomorrow. We expect to get a little wind and waves and maybe some rain.

“We have 100 instruments on the ship running all the time,” with 18 pairs of eyes glued to them for clues to how the mysterious rivers work, even as waves toss the ship violently up and down.