June 17, 1998


In an effort to better understand clouds and how they affect our environment, a NASA DC-8 aircraft is flying this week carrying an airborne radar system designed to study the structure of clouds, including cloud liquid water content.

During the current flights over the southern United States, NASA's Airborne Cloud Radar is looking at clouds in an attempt to better understand how clouds warm or cool Earth's atmosphere and how the presence of clouds influences the world's climate.

"Clouds represent a scientific puzzle that researchers have been trying to piece together for centuries," said Dr. Fuk Li, the principal investigator for the cloud radar at NASA's Jet Propulsion Laboratory, Pasadena, CA. "Scientists still don't know very much about the internal, vertical structures of clouds, and that leads to uncertainties in weather and climate predictions. Using the cloud radar, we will be able to study clouds in a new way that will help us understand their structure like never before. Once we have the cloud vertical structure information, atmospheric scientists will have a much better handle on long-term predictions of weather and climate change."

The cloud radar experiment was installed last month looking downward in the tail area of the DC-8, based at NASA's Dryden Flight Research Center, Edwards, CA. The DC-8 then flew to Tinker Air Force Base near Oklahoma City, OK, the origination point of this series of missions in which the radar collects cloud data while the plane flies above the clouds.

Scientists will compare these data with measurements taken by satellite and ground-based sensors, including the Department of Energy's Southern Great Plains Cloud and Radiation Testbed, a series of instruments spread across north central Oklahoma and south central Kansas.

The radar, taking vertical measurements of the clouds from above, operates at 94 gigahertz, making it sensitive to cloud particles. The instrument transmits radar energy, which bounces off the cloud particles and is reflected back towards the aircraft. The radar measurements will be combined with information provided by other sensors to help analyze the properties of the clouds observed.

This experiment has flown twice before aboard the DC-8 while still under development. The DC-8's unique features make it an ideal platform for examining cloud structures, according to DC-8 mission manager Chris Jennison of Dryden.

"The DC-8 was selected because it is the only aircraft that is capable of this mission in terms of altitude, speed, range and capacity for carrying scientists onboard. Since scientists can fly on the aircraft, they can operate their experiments themselves," Jennison said.

This Airborne Cloud Radar flight series is expected to total 20 flight hours. The experiment is designed to test several hypotheses and techniques related to satellite remote sensing of extensive, long-lasting, non-precipitating layers of cloud in the middle and upper troposphere -- atmosphere up to about 11 kilometers (seven miles) from Earth's surface.

It is expected that this instrument will be used in upcoming field experiments to better understand cloud-climate processes. One such planned experiment is the Tropical Cirrus Experiment called CRYSTAL planned for 2001. Eventually this instrument will be flown on satellite platforms designed to observe Earth's climate processes from space.

The Jet Propulsion Laboratory, a division of the California Institute of Technology, developed the Airborne Cloud Radar in conjunction with the University of Massachusetts, Amherst; Colorado State University, Ft. Collins; and Pennsylvania State University, Philadelphia.

The Airborne Cloud Radar is part of NASA's Earth Science enterprise, a long-term research program designed to study Earth's land, oceans, atmosphere, ice and life as a total integrated system.

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