Researchers collect rare data linked to rain and drought

From left to right: The G-IV, P-3, and G-1 aircraft at McClellan Airfield in Sacramento, California, prepare for a coordinated flight mission. Photo courtesy of Marty Ralph, Scripps Institution of Oceanography at University California, San Diego.
From left to right: The G-IV, P-3, and G-1 aircraft at McClellan Airfield in Sacramento, California, prepare for a coordinated flight mission. Photo courtesy of Marty Ralph, Scripps Institution of Oceanography at University California, San Diego.

After six weeks of gathering data from air and sea in California, scientists are back on dry land ready to examine their findings. In January 2015, the Atmospheric Radiation Measurement (ARM) Climate Research Facility launched the ARM Cloud Precipitation Experiment (ACAPEX), the largest study of its kind focused on capturing data from atmospheric rivers. These rivers are narrow bands of enhanced water vapor associated with the warm sector of tropical cyclones over the Pacific and Atlantic oceans.

Atmospheric rivers account for 30 to 50 percent of the annual precipitation in California. These precipitation processes can be influenced by different sources of aerosol particles, and scientists need data to understand how various aerosols interact to create rain or drought. The team, led by Ruby Leung at Pacific Northwest National Laboratory (PNNL), chased and sampled a total of four atmospheric rivers that made landfall in northern California during ACAPEX, and collected data from instrument ground stations throughout the state, in hopes of getting closer to answering these precipitation questions.

The Weather Waits for No One

The team coordinated the G-1 aircraft to rendezvous with the Ron Brown ship during an atmospheric river over the Pacific Ocean. The G-1 was traveling at 1,000 feet above the ocean and cloud base.
The team coordinated the G-1 aircraft to rendezvous with the Ron Brown ship during an atmospheric river over the Pacific Ocean. The G-1 was traveling at 1,000 feet above the ocean and cloud base.

It’s hard to be a storm chaser when there are no storms—but the small three, and single large, atmospheric rivers that passed through California were caught. It wasn’t just luck. A key to success was the ability to use several platforms at once to collect the rare data.

Four aircraft—the National Oceanic and Atmospheric Administration (NOAA) WP-3D and Gulfstream-IV (G-IV), the National Aeronautics and Space Administration (NASA) ER-2, and the U.S. Department of Energy (DOE)-sponsored Gulfstream-1 (G-1)—and NOAA’s research ship, the Ronald H. Brown, collected data at all different altitudes and route patterns.

"During the one really big atmospheric river storm, I was on the G-1 participating in the data collection across five different research flights," said Leung. "I could look down below the clouds and see the ship directly below the atmospheric river. It was then that I knew we were collecting some good stuff. It was very exciting."

Aircraft and ship flight patterns are shown here during an atmospheric river occurrence in February 2015 over the California coast.
Aircraft and ship flight patterns are shown here during an atmospheric river occurrence in February 2015 over the California coast.

A Big Can of Mixed Soup

"We observed all kinds of aerosols being transported, even dust and sometimes biomass burning aerosols from agricultural fires that appear to be transported from Asia," said Leung.

The team learned that there are many aerosol types that mix during these atmospheric rivers. All of these particles were mixing like a batch of soup made from scratch. Just like an ingredient changes a soup's flavor, each of these aerosol particles have different effects on clouds.

This campaign consisted of several principal and co-principal investigators who are world-renowned in aerosol research and instrumentation. ACAPEX included collaborators from PNNL; NOAA; Scripps Institution of Oceanography at University California, San Diego; Colorado State University; the Hebrew University of Jerusalem; Los Alamos National Laboratory, Argonne National Laboratory, Brookhaven National Laboratory, and Stratton Park Engineering Company. The ARM team worked in conjunction with the CalWater2 field campaign, led by NOAA, that sponsored two of the aircraft and the research ship that hosted the U.S. DOE’s second ARM Mobile Facility (AMF2).

In addition to atmospheric rivers, ACAPEX also collected aerosol and cloud data in different environments. It will take time to process all of the collected data from the ACAPEX and CalWater2 campaigns. Over the next few years, the team will use the data to evaluate regional and global climate models and understand how aerosol-cloud interactions influence precipitation.

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The ARM Cloud Aerosol Precipitation Experiment is sponsored by the U.S. Department of Energy through the Office of Science's Office of Biological and Environmental Research and an integral part of CalWater 2015. CalWater 2015 is an interagency, interdisciplinary field campaign combining the resources of CalWater2 and ACAPEX. The CalWater 2015 research team includes scientists from Scripps Institution of Oceanography at University California, San Diego, the Department of Energy's Pacific Northwest National Laboratory, NOAA, and NASA.

The ARM Climate Research Facility is a national scientific user facility funded through the U.S. Department of Energy's Office of Science. The ARM Facility is operated by nine Department of Energy national laboratories.