JPL Airborne Sensor to Study 'Rivers in the Sky'

Feature Feb. 10, 2011

JPL Airborne Sensor to Study 'Rivers in the Sky'

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-048&cid=release_2011-048

They're called atmospheric rivers — narrow regions in Earth's atmosphere that
transport enormous amounts of water vapor across the Pacific or other regions. Aptly
nicknamed "rivers in the sky," they can transport enough water vapor in one day, on
average, to flood an area the size of Maryland 0.3 meters (1 foot) deep, or about seven
times the average daily flow of water from the Mississippi River into the Gulf of Mexico. The phenomenon was the subject of a recent major emergency preparedness scenario led by the U.S. Geological Survey, "ARkStorm," which focused on the possibility of a series of strong atmospheric rivers striking California — a scenario of flooding, wind and mudslides the USGS said could cause damages exceeding those of Hurricane Katrina in 2005.

While atmospheric rivers are responsible for great quantities of rain that can produce
flooding, they also contribute to beneficial increases in snowpack. A series of
atmospheric rivers fueled the strong winter storms that battered the U.S. West Coast
from western Washington to Southern California from Dec. 10 to 22, 2010, producing 28 to 64 centimeters (11 to 25 inches) of rain in certain areas. The atmospheric rivers also contributed to the snowpack in the Sierras, which received 75 percent of its annual snow by Dec. 22, the first full day of winter.

To improve our understanding of how atmospheric rivers form and behave and
evaluate the operational use of unmanned aircraft for investigating these phenomena,
NASA scientists, aircraft and sensors will participate in a National Oceanic and
Atmospheric Administration-led airborne field campaign slated to begin Feb. 11.

Called Winter Storms and Pacific Atmospheric Rivers, or WISPAR, the field campaign,
which continues through the end of February, is designed to demonstrate new
technology, contribute to our understanding of atmospheric rivers and assist NOAA in
potentially conducting offshore monitoring of atmospheric rivers to aid in future
weather predictions.

A NASA Global Hawk unmanned aircraft operated out of NASA's Dryden Flight
Research Center in Southern California is scheduled to depart Dryden Friday
morning, Feb. 11, on the campaign's first science flight. The 24-hour flight will study
an atmospheric river currently developing in the Pacific Ocean off Hawaii that appears
as though it will impact the Oregon-California coast this weekend. Aboard the Global
Hawk will be new weather reconnaissance devices called dropsondes developed by
the National Center for Atmospheric Research that will take temperature, wind and
other readings as they descend through an atmospheric river. Also aboard will be an
advanced water vapor sensor — the High-Altitude Monolithic Microwave Integrated
Circuit Sounding Radiometer, or HAMSR — created by NASA's Jet Propulsion
Laboratory in Pasadena, Calif.

The remote-sensing HAMSR instrument analyzes the heat radiation emitted by oxygen
and water molecules in the atmosphere to determine their density and temperature. The instrument operates at microwave frequencies that can penetrate clouds, enabling it to determine temperature, humidity and cloud structure under all weather conditions. This capability is critical for studying atmospheric processes associated with bad weather, like the conditions present during atmospheric river events.

HAMSR Principal Investigator Bjorn Lambrigtsen of JPL says the instrument — the
most accurate and sensitive of its kind in the world — will help scientists better
understand these unique weather phenomena.

"The WISPAR campaign is intended to study the concentrated streams of tropical
moisture that sometimes get connected with cold fronts and winter storms approaching
the U.S. West Coast — sometimes called the pineapple express, since they often
originate near Hawaii — which can result in very intense rain events," Lambrigtsen
said. "HAMSR, flying on NASA's unpiloted Global Hawk well above the weather but
close enough to get a much more detailed picture than is possible from a satellite, will
be used to map out this phenomenon and answer scientific questions about the
formation and structure of these systems."

NASA's Global Hawk is an ideal platform from which to conduct WISPAR science
because it is able to fly long distances, stay aloft for more than 24 hours and travel at
high and low altitudes that could be dangerous for humans. Lambrigtsen will be at
Dryden in the Global Hawk Operations Center during the flights, using data from the
sensor and other information to adjust the Global Hawk's flight track, as necessary, to
optimize the sampling of the atmospheric rivers.

Lambrigtsen said the public can monitor the progress of the WISPAR science flights in
real time on a WISPAR version of JPL's hurricane portal website at
http://winterscience.jpl.nasa.gov/WISPAR2011/ . The site will display the most recent
satellite images, the Global Hawk flight track and a real-time subset of HAMSR data.

For more information about WISPAR, visit:
http://www.noaanews.noaa.gov/stories2011/20110210_atmosphericrivers.html . For
more on HAMSR, see: http://microwavescience.jpl.nasa.gov/instruments/hamsr/ .

Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov

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