Experiment studying major West Coast winter storms – Atmospheric Rivers – kicks off this week in California

This week, as planes begin flying through storm clouds over the California coast, a ship set sail from Hawaii towards a destination in the northeastern Pacific. Their passengers aren’t commercial travelers or a pleasure cruisers, but the scientists and sensors involved in CalWater 2015, a two-month research study to investigate how West Coast rain and snow are impacted by atmospheric rivers (intense moisture-bearing winter storms) and aerosols (particles such as dust and pollution).

“Improving our understanding of atmospheric rivers will help us produce better forecasts of where they will hit and when, and how much rain and snow they will deliver,” says Allen White, a research meteorologist at NOAA’s Earth System Research Laboratory (ESRL) and CalWater 2015 mission scientist.

atmospheric river

Atmospheric rivers (ARs) are narrow conveyor belts of water vapor in the atmosphere that can extend thousands of miles and are responsible for delivering much of the water vapor associated with major storms along the West Coast. In California, it's critical to understand if precipitation will arrive as snow–often good news, because it can 'store" water in slow-melting mountain snowpack–or rain, which can increase flood risk.

Continues White, “Better forecasts will give communities the environmental intelligence needed to respond to droughts and floods.”

The other important piece of the study is aerosols. These particles can come from local sources or remote continents, and can directly influence western U.S. precipitation and how storms develop. When moisture from a landfalling AR is lofted by mountains, aerosols aloft can provide the "seeds", which can enhance precipitation.

Lead scientists from NOAA/ESRL’s Physical Sciences Division (including STC and CIRESresearchers) and colleagues from the ESRL Chemical Sciences Division (CSD) and other government agencies, university, and private industry will collect a variety of measurements from instruments aboard four research aircraft and a NOAA research ship, as well as land-based observations from NOAA Hydrometerology Testbed (HMT) field sites across California.

"It is rare that such an array of observing platforms are devoted to a field campaign," says White. "It’s both an exciting opportunity and a challenge to coordinate and make optimal use of these assets."

The combined air, ship, and land-based measurements will help researchers understand the scientific ingredients that contribute to atmospheric rivers. This information can be used to improve short- and long-term predictions of precipitation, and to develop decision support tools for extreme precipitation events, hazard response, and water supply for more effective water resource management.

Janet Intrieri boards the NOAA G-IV

In the air…
Flying out of McClellan Airfield in Sacramento, CA, NOAA’s P-3 and G-IV (aka Hurricane Hunters), and the DOE G-1 aircraft, and the NASA ER-2 out of Palmdale, CA will each carry specialized sensors to measure temperature, relative humidity, wind speed and direction, cloud properties, aerosol chemistry, ozone, and even ocean temperature, among other things.


R/V Ron Brown

In the ocean…
Leaving port on January 14th, the NOAA ship Ronald H. Brown began its trek from Hawaii to a targeted region off the California coast. Once there, the ship can be navigated within sight of any ARs in the region. Researchers aboard the Ron Brown will operate NOAA and DOE instruments, and release weather balloons and ozonesondes to study the interaction between the ocean and atmosphere and how it influences atmospheric rivers.

Tom Ayers at Bodega Bay

On the ground…
HMT has been monitoring atmospheric rivers for years at field sites across California, and for CalWater 2015 will contribute land-based measurements of precipitation, winds, snowpack, soil moisture, snow level, and surface weather. Also, the National Science Foundation is supporting the Scripps and Colorado State University to install additional instrumentation at HMT’s Bodega Bay site to study aerosol chemistry.

Lead agencies for CalWater 2015 include NOAA, the U.S. Department of Energy (DOE)Scripps Institution of Oceanography, the National Aeronautics and Space Administration (NASA), the Naval Research Laboratory (NRL) and the National Science Foundation. DOE’s Atmospheric Radiation Measurement (ARM) program has committed air and ship borne facilities for this same period in a study called ACAPEX (ARM Cloud Aerosol and Precipitation Experiment), a complementary study to CalWater 2015. A list of additional partners can be found on the CalWater 2015 website.

Related Links


  • Chris Fairall, research physicist, NOAA/ESRL Physical Sciences Division, 303.497.3253
  • Ryan Spackman, flight operations scientist, NOAA/ESRL Physical Sciences Division, 303.497.7873
  • Allen White, research meteorologist, NOAA/ESRL Physical Sciences Division, 303.497.5155
  • Monica Allen, Media Relations, NOAA/OAR, 301.734.1123
  • Barb DeLuisi, Communications, NOAA/ESRL Physical Sciences Division, 303.497.4233