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July 21, 1999

John Bluck

NASA Ames Research Center, Moffett Field, CA

(Phone: 650/604-5026)


Allen Kenitzer

NASA Goddard Space Flight Center, Greenbelt, MD

(Phone: 301/286-2806)


Leslie Mathews

NASA Dryden Flight Research Center, Edwards, CA

(Phone: 661-258-3893)


Steve Roy

NASA Marshall Space Flight Center, Huntsville, AL

(Phone: 256-544-6535)




The world's largest atoll will be the site of a two-month experiment that is part of a NASA-led effort to better understand tropical rainfall in order to improve weather forecasting and long-term climate modeling.

More than 200 experts from NASA, other government agencies, universities and research institutions are traveling this month to the remote atoll, Kwajalein, a chain of coral islands that surround a 1,000 square mile lagoon. The atoll is part of the Republic of Marshall Islands in the tropical Pacific Ocean.

The experiment, called KWAJEX, is part of a bigger NASA Tropical Rainfall Measuring Mission (TRMM), during which scientists throughout the world are gathering detailed weather data on the ground, by airplane, ship and balloon. Researchers will calibrate instruments on board the mission's TRMM satellite and gather detailed weather data the satellite cannot obtain remotely. KWAJEX is the last of a series of experiments conducted as part of TRMM.

"NASA and the Japanese National Space Development Agency launched the TRMM satellite from which we'll get global precipitation measurements," said Steve Hipskind, Chief of the Atmospheric Chemistry and Dynamics Branch at NASA's Ames Research Center, Moffett Field, CA. By measuring tropical rainfall, scientists hope to get a better overall picture of how the Sun's energy, which is concentrated in the tropics, is transferred from the ocean to the atmosphere.

A better understanding of the energy transfer that drives the atmospheric motion, will help scientists improve global computer models to better forecast weather and long-term climate change.

"We can improve our global computer models of how weather and our long-term climate might be affected not only by human activities, but by natural phenomena such as El Niño as well," said TRMM Program Scientist Ramesh Kakar of NASA Headquarters, Washington, DC. "While Kwajalein is very remote and logistically difficult, Kwajalein presents the ideal location for studying oceanic rainfall due to its location in the middle of the Pacific and its lack of any mountains or even hills that can cause their own small scale weather."

"With its radar and microwave instruments, the satellite obtains a large-scale view of precipitation, but with less detail than many surface-based instruments. In contrast, ground and airborne measurements allow us to really understand the three-dimensional structure and evolution of tropical storm systems," Hipskind said. "Even without the satellite, these field experiments are leading to significant scientific progress in understanding precipitation processes."

The goals of the experiment are to better understand the exact nature of oceanic rainfall and how it differs from rain over land. "We know from the TRMM observations, for instance, that thunderstorms tend to be much weaker over oceans than over land," said TRMM Project Scientist, Chris Kummerow of NASA Goddard Space Flight Center, Greenbelt, MD. "These differences in the clouds and possibly down to the raindrops themselves must be understood first and then accounted for in the satellite measurements if credible rainfall estimates are to made around the globe."

NASA Ames is responsible for KWAJEX project management and logistics. Ames has also managed three TRMM validation missions to Texas, Florida and Brazil. "Our job during KWAJEX is to synthesize the scientific objectives and the detailed requirements the scientists have, and from those develop and implement the overall project plan," Hipskind said.

"When scientists first put together the plan for the satellite, they also made a ground observation plan," Hipskind said. The plan supplements satellite observations with detailed measurements of clouds. The plan included setting up long-term measuring stations at numerous locations around the globe.

"Once you are able to establish the relationship between what the satellite is seeing and what is happening in detail in the atmosphere, then you can have confidence in the satellite measurements on a global scale," Hipskind said.

"There are three instrumented aircraft scheduled to fly during the experiment: the DC-8 `Flying Laboratory' from NASA Dryden Flight Research Center, Edwards, CA; a Cessna Citation II from the University of North Dakota and a twin-engine Convair 580 from the University of Washington, Seattle," said Wendy Dolci of Ames who serves as co-project manager with Hipskind.

The DC-8 will serve two roles for the experiment. That aircraft will simulate satellite overpasses by flying above clouds with the same instruments that are aboard the TRMM satellite – a radar and radiometers. The DC-8 will also collect data from within clouds, using cloud particle imagers and sampling equipment to measure vapor, liquid, and solid particle size, temperature, density and motion within clouds.

A newly commissioned National Oceanic and Atmospheric Administration (NOAA) research vessel, The Ron Brown, will make additional observations. "Two of our key instruments are meteorological Doppler radars on Kwajalein and on the Ron Brown," Hipskind said. When combined, the two Doppler radars can be used to measure the three-dimensional motions of cloud droplets, he explained.

KWAJEX will involve scientists, engineers and technicians from several NASA centers, other agencies including NOAA and the National Science Foundation and many universities as well as private research companies. Some participants also come from Germany, United Kingdom, France, Croatia, Canada, Australia, Austria, South Korea, Japan, New Zealand, India and Turkey. The KWAJEX experiment will continue through September 15.

In addition to Kwajalein, other TRMM weather observation locations are Thailand; Taiwan; Israel; Guam; Darwin, Australia; Hawaii; Texas; Florida and Brazil. TRMM is part of NASA's Earth Science Enterprise, a long-term research program designed to study the Earth's land, oceans, air, ice and life as a total system and the effects of natural and human-induced changes on the global environment.

TRMM is managed by NASA's Goddard Space Flight Center, Greenbelt, MD, for NASA's Office of Earth Science, Washington, DC. Images from the TRMM mission are available on the Internet at URL:

Other websites related to KWAJEX include:

NASA Ames -

NASA Dryden DC-8 –

NOAA's R.H. Brown site --

University of Washington --

UND Citation –



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