New satellite-generated rain maps provide improved look at tropical rainfall

December 17, 2000

New detailed satellite-generated rain maps paint a more accurate picture of how much rain falls in the tropics. These new maps provide more accurate tropical rainfall measurements and may enable better management of water resources, may provide clues to developing El Niños and La Niñas, and give scientists a better understanding of how latent heat generated from tropical rains influences weather around the world.

Robert Adler of NASA's Goddard Space Flight Center in Greenbelt, Md., will present new detailed rain maps from data gathered by NASA's Tropical Rainfall Measuring Mission (TRMM) satellite at a press briefing during the American Geophysical Union's Fall meeting. The meeting will be held at the Moscone Center in San Francisco, and the briefing titled "New Findings from TRMM" will be held on Monday, December 18 at 9:00 a.m. (Pacific Time) in Room 112.

The TRMM rain maps incorporate both high-resolution microwave and precipitation radar data, and depict monthly rainfall since1998 over an area from 38 degrees North latitude to 38 degrees South.

"Before TRMM, there was a great degree of variability in monthly rainfall estimates," says Marshall Shepherd, Goddard research meteorologist. The measurements from TRMM are helping to improve that situation, although it will take further analysis to fully utilize the data.

TRMM monthly rainfall maps are produced by a team of Goddard scientists led by Adler, the TRMM Project Scientist, which merges the TRMM Microwave Imager (TMI), Precipitation Radar (PR), geosynchronous infrared data and rain gauge data. Monthly rain maps produced in this manner are thought to provide more accurate rainfall totals by exploiting the strengths of multiple data sources.

According to Adler, "This technique uses TRMM to calibrate or adjust the rain estimates from the other satellites which are not as accurate, and provides more 'looks' at the rainfall systems which can vary very rapidly. Adler said that scientists are "using TRMM as a 'flying rain gauge' and exploiting its more accurate measurements along with the additional satellite information to provide the most complete rainfall estimate."

Another important result of TRMM's rain maps is the ability to see changes in rainfall amounts over a region. "These rainfall anomalies help to clearly identify flooded and dry regions and how they may be tied into other processes," Adler said. His findings show a strong correlation between abnormally high rainfall in the eastern Pacific Ocean and a developing El Niño, and unusually low rainfall in that region tied to developing La Niñas.

Because El Niños and La Niñas have a major impact on flooding and drought distribution around the world, Adler's findings have implications for better water resource management in the future. The findings will also assist in planning disaster relief and preparations for vector-borne disease outbreaks when flooding and extreme heat is predicted.

"These rain maps have implications for understanding how latent heating in the tropics affects weather and climate circulations. Rainfall is a signature of the latent heat energy, that 'fuels' global wind circulation," Shepherd noted. Armed with more accurate global rainfall information, scientists also hope to improve the accuracy of short-term weather forecasts and longer-term climate projections.

TRMM is a joint U.S.-Japanese mission and 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. The TRMM satellite was launched on November 27, 1997.
More information, animations, and images of the TRMM rainfall maps are available at: Rob Gutro/ Harvey Leifert
AGU Press Room
(Phone: 415/ 905-1007)

NASA/Goddard Space Flight Center

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