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Tropical rains help predict global weather
September 2, 1999  If it rains over the ocean, can we feel the outcome on land? Yes we can, but until recently, no weather data was collected over the ocean. A series of experiments, measurements and data collecting events have taken place since November 1997 in the tropics and subtropics, helping weather forecasters improve their predictions. "Rain over water affects the climate of the whole planet," said Robbie Hood of the Global Hydrology and Climate Center. "It releases energy into the atmosphere. What happens in the tropics is extremely important to the climate of the whole Earth. If you can't measure rain over the ocean, you're missing a lot of activity and you'll never truly understand what is happening to the weather across the world." In November 1997, NASA and Japan's National Space Development Agency launched the Tropical Rainfall Measuring Mission satellite to develop methods to measure rainfall in the tropics and subtropics. TRMM takes about 91 minutes to complete its orbit, allowing 16 orbits in one 24-hour period. The TRMM measurements are used to find out where it's raining and how hard. Not all clouds cause rain and when rain does fall, it goes through various layers in the atmosphere, sometimes never reaching the ground. Being able to know how rainfall happens and why will help atmospheric scientists and weather forecasters predict droughts, floods, wind patterns and ocean currents. The scientists studying the data needed a way to correctly interpret the information TRMM was sending them. So, a new mission has begun — the Kwajalein Experiment known as KWAJEX. "The TRMM team wanted field experiments from the very beginning because it knew there would be issues about validating the results from the satellite," said Dr. Eric Smith director of the GHCC. KWAJEX is operated out of the Kwajalein Atoll, a U.S. Army missile test site. Scientists there are using instruments aboard three aircraft and a ship to measure rain in and under thunderstorms over the open ocean. Their plan of attack will be timed to coincide (when possible) with overflights by the TRMM satellite. Since it began July 23, KWAJEX has flown at least 18 aircraft missions and runs through Sept. 15 in the central Pacific Ocean. "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 Dr. Ramesh Kakar, the TRMM program scientist at NASA Headquarters in Washington, D.C.
The scientists will also launch radiosondes, instrument-bearing balloons that report readings of temperature, moisture and winds as they ascend through clouds, from several islands surrounding the atoll. To the southwest of Kwajalein Island, the National Oceanic and Atmospheric Administration research vessel Ronald H. Brown will watch with a doppler radar similar to a unit on Kwajalein. From this data, scientists can assemble true 3-D models of rain motion. In addition to balloons and radar on Kwajalein as well as the research vessel, KWAJEX will use the University of Washington's Convair 580 and the University of North Dakota's Cessna Citation. "We are bringing in microphysics aircraft with special instruments," Smith said. "In that same context, we're going to do vertical profiles, the Holy Grail for cloud researchers for years, to get vertical slices of cloud microphysics. We've never had an experiment designed to do that over the deep ocean." The Kwajalein area, the world's largest atoll and part of the Republic of Marshall Islands, is representative of much of the open ocean and the atolls are so small they should have no influence on rain systems, according to Smith. Copyright 1999, Environmental News Network, All Rights Reserved RELATED STORIES: Clouds' illusions attract ocean weather study RELATED ENN STORIES: Study targets Gulf Stream-fueled weather
RELATED SITES: KWAJEX Operations Center
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