A New Eye in the Sky for Studying Rain

TOKYO — Will global warming really spark global catastrophe? How much damage will El Nino cause? Which areas of the Earth will be most affected by such climatic events, and when?

One of the stumbling blocks scientists face in answering such questions turns out to be an inadequate understanding of rain.

Inaccurate and incomplete data about rainfall and its atmospheric consequences, especially in the tropics, where more than two-thirds of the Earth’s precipitation occurs, are major obstacles to improving the complex supercomputer models that are used for global climate forecasting.

Next week, in a notably harmonious collaboration between NASA and Japan’s space agency, a special weather satellite specifically designed for climate research will be launched from an island in southern Japan.

The Tropical Rainfall Measuring Mission, known by the initials TRMM, consists of a U.S.-built satellite observatory carrying a Japanese-built precipitation radar device--the first ever designed to measure rainfall from space--as well as four other specialized instruments.

The entire 7,920-pound, $700-million package will blast off aboard a Japanese H-II rocket, the launch engine for Japan’s increasingly cutting-edge space program, on Wednesday from the Japanese space center at Tanega Shima, off the southern coast of Kyushu.

Japan is launching another satellite aboard the same rocket to do research on robotics, said Mamoru Endo, manager of the policy department at the National Space Development Agency of Japan, or NASDA.

Because the satellite is so heavy and because its orbit at an altitude of 217.5 miles is unusually low, it will probably stay aloft for just three years, NASA and NASDA scientists said. Special materials had to be developed to shield the observatory from a layer of atomic oxygen that tends to corrode and erode objects orbiting at that level.

The satellite, which is the result of more than 10 years of cooperation between the U.S. and Japan, will be able to observe and measure the effects of such events as this year’s unusually strong El Nino and the Indonesian forest fires that have blanketed much of Southeast Asia in haze, said Tasuku Tanaka, director of the Earth Observation Research Center at NASDA. Among other things, the data will improve forecasting of the arrival of Asian monsoons.

Although humans have been measuring rainfall since at least 350 BC in India, global rainfall mapping is still much cruder than the everyday wizardry of TV satellite weather photos might lead viewers to assume.

“Everybody knows it can rain on one side of the street and not the other,” said Joanne Simpson, chief scientist for meteorology at NASA’s Goddard Space Flight Center in Greenbelt, Md. However, most tropical rain falls unobserved into oceans or jungles, while land monitors, she said, tend to be on islands, which alter rainfall patterns.

Tropical rainfall is crucial to understanding the climate--and the “greenhouse effect”--because most solar heating of the Earth occurs in the tropics. When the water that evaporates into clouds condenses into rain, it releases huge amounts of latent energy into the upper atmosphere that in turn creates wind.

However, the satellites that monitor rainfall tend to be in orbits where they pass over the same part of the Earth at the same time each day, making them less than ideal for measuring tropical precipitation, which often varies within a day. TRMM will orbit the Earth about 16 times a day, passing over each area at many different hours.

Simpson, who in 1949 was the first U.S. woman to earn a PhD in meteorology, said she is thrilled to be working on the mission because she has spent 50 years studying clouds, first by flying through them in aircraft to test her theories then using satellite data and computers.

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An Orbiting Rain Gauge

* Project: Tropical Rainfall Measuring Mission, a U.S.-built satellite observatory carrying a Japanese-built precipitation radar device.

* Goals: Collect accurate data on global rainfall, shed light on how rain releases heat energy to drive atmospheric circulation, help improve models of global climate change.

* Cost: About $700 million, of which about $200 million is paid by Japan.

* Background: Venture is part of NASA’s Mission to Planet Earth program to study Earth as an environment system. It is the second U.S.-Japanese Earth research satellite project.

* internet site: https://trmm.gsfc.nasa.gov

Source: U.S. National Aeronautics and Space Administration