The Tropical Rainfall Measuring Mission (TRMM) satellite, the world’s first space mission dedicated to observing and understanding tropical rainfall, has successfully completed its fourth year of continuous data gathering by providing exciting new insight into tropical and global rainfall and hurricanes.

Initially designed as a three-year mission, the orbiter is continuing to collect a variety of measurements which are being used to answer a diverse array of key climate and weather questions related to Earth’s hydrological cycle. These questions range from microscopic processes that control the formation of snowflakes and raindrops inside clouds, to the shifting global-scale patterns of El Niño rainfall. The TRMM satellite provides valuable insights into the processes that energize city-sized thunderstorm clouds and other violent storms, such as hurricanes and monsoon rains over Southeast Asia.

“The vast range of rainfall processes being studied by TRMM, from the scale of the entire Earth down to one millionth of a meter, is akin to a physician’s study of the human body, beginning with the organism as a whole and progressing downward to the molecular level of DNA,” stated Dr. Jeff Halverson, TRMM Education and Outreach Scientist at NASA’s Goddard Space Flight Center, Greenbelt, Md.

TRMM science has recently revealed some exciting and startling insights at all of these levels of analysis. On one end of the science spectrum, the international team of TRMM investigators is learning about the ways in which countless tiny cloud particles less than 1 mm across interact inside clouds to produce rain. With the satellite flying overhead, specially equipped research aircraft probe the cloud interiors with sensitive cloud particle detection equipment. One crucial finding is that microscopic dust and soot particles, which commonly arise from polluted air, can interfere with this process of rain formation. The findings indicate that “dirty” clouds are less likely to produce rain than their cleaner-air counterparts, thus influencing studies of pollution and climate interaction.

On the larger scale of rain clouds themselves, insights are being discovered into why there is a tendency for heavy rains to fall primarily over heated tropical land masses by day, but over the vast ocean regions mainly at night. In addition, it is now known that the greatest concentration of lightning on the Earth is centered over the African Congo. The reasons for this lightning pattern remain unclear, but solving this puzzle is nevertheless critical for understanding how the global electrical circuit operates.

At the global climate scale, migrating rainfall patterns across the Pacific Ocean during El Niño and La Niña episodes are being mapped with a greater degree of accuracy than ever before possible, which can lead to better prediction of droughts and floods around the world. By combining the TRMM rainfall data with other new satellites that map winds and atmospheric temperature structure, scientists are discovering key new processes that lead to the birth and intensification of deadly tropical storms, discoveries that may help in storm prediction.

Launched in 1997, the TRMM satellite received a new lease on life in August 2001, when it was boosted into a higher orbit to extend its life. Halverson said it is anticipated that the TRMM satellite will remain fully operational for up to six years, so the prospects for further discoveries about rainfall and its impacts on society remain excellent. These discoveries, when combined with oceanic and atmospheric data from other existing and planned satellites from NASA and the National Oceanic and Atmospheric Administration (NOAA), are expected to yield fresh insights into how the Earth’s water, land and atmospheric systems interact to create both the everyday-type rainfall systems and rare catastrophic flood events. These data about the Earth’s water cycle will then help meteorologists make improvements to forecasts, and help climatologists better understand how the global climate is changing.

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.

Extensive video resource material is available on the TRMM mission. For more information, please contact Rachel Weintraub at 301-286-0918.

Information and images from the TRMM mission are available on the Internet at: