ScienceDaily (Sep. 21, 2006) — How can one know how much rain really falls over the path of a tropical storm or hurricane? This is a question that greatly interests meteorologists and hydrologists. On their behalf, and on behalf of the public which ultimately benefits from better observations of storms, NASA scientists are using satellite data from its rain gauge in space, the Tropical Rainfall Measuring Mission or “TRMM” to help provide these measurements.

TRMM, a joint mission between NASA and JAXA, the Japanese Space Agency, was launched in 1997 to study rainfall in the tropics. Since then, researchers and forecasters have found TRMM invaluable. TRMM has provided rainfall data in places that have no rain gauges, as well as lightning data and a never before seen 3-D look into storms. That 3-D capability has also led scientists to formulate a theory on "Hot Towers," or towering clouds that form in the eyewall of a hurricane.

Currently, scientists are using TRMM data to provide a complete picture of precipitation around the entire world. Goddard scientists Bob Adler and George Huffman are compiling this information using TRMM, as well as data from NASA’s Aqua satellite, a few Department of Defense satellites, a few National Oceanic and Atmospheric Administration polar-orbit satellites, and five international geostationary-orbit satellites. Polar orbiting satellites fly over the north and south poles. Geostationary satellites are those that orbit the Earth in a fixed position over the Equator.

This combination of satellite data allows Adler and Huffman to compute how much rain has fallen over three hour periods for most of the world, not including the upper northern and lower southern hemispheres. Huffman said "Data from TRMM are key to getting the complete picture of rainfall around the world, because of the satellite's high quality sensors and special orbit." Adler and Huffman take advantage of these attributes to adjust each of the other satellite data sets to TRMM's rainfall data.

NASA uses these TRMM Multi-satellite Precipitation Analysis data to create maps of rainfall accumulation along the tracks of hurricanes.

This image shows the amount of rain that fell from Hurricane Ernesto from Aug. 24 to Sept. 1, 2006. The rainfall is accumulated within approximately 410 miles (a radius of 6 degrees) from the storm's center along the track. The track line is superimposed on the rainfall, with the storm intensity indicated by the color of the line. (Image courtesy of NASA/Goddard Space Flight Center)

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