Scientists have discovered that thunderstorms over tropical lands can act like ocean storms, pollution can inhibit rainfall, and upper level winds may determine the characteristics of thunderstorms.

Some of these findings give promise to better understanding thunderstorm development, and researchers working with NASA�s Tropical Rainfall Measuring Mission (TRMM) satellite will discuss them in a press briefing at the upcoming meeting of the American Geophysical Union (AGU) in San Francisco on December 18.

Three panelists will discuss how TRMM has revealed that clouds over tropical land areas sometimes take on characteristics of maritime clouds, which are more efficient producers of warmer rains. They will also discuss how polluted air causes less efficient rain-producing clouds, how upper level wind direction may be a key to determining thunderstorm characteristics, and they will present new comprehensive 2-year rainfall maps that will help researchers better understand tropical rainfall.

A panel of scientists working on the TRMM mission will present their findings at a press briefing on Monday, December 18, at 9:00 a.m. Pacific Time in Room 112 of the Moscone Center in San Francisco, Ca.

Wei Kuo Tao of NASA's Goddard Space Flight Center in Greenbelt, Md., will introduce the panelists: Daniel Rosenfeld, Edward Zipser, and Robert Adler.

Daniel Rosenfeld, a member of the TRMM science team and a professor at the Hebrew University of Jerusalem, will present findings from Amazonia on man-made aerosols and burning; Edward Zipser from the University of Utah will present findings of thunderstorm development over tropical oceans and continents; and Robert Adler, the TRMM project scientist from NASA�s Goddard Space Flight Center, will discuss new rain maps and anomalies in rainfall.

One of TRMM�s functions is to document the detrimental impact of smoke, air pollution, and desert dust on precipitation. "Global atmospheric circulation patterns are very sensitive to the inhibition of rainfall by smoke and other types of air pollution," said Rosenfeld. "By monitoring and understanding the impact of smoke and air pollution on rainfall, we will be able to better manage and protect our water resources."

Zipser will discuss how TRMM data in conjunction with other data sets taken during four-month wet-seasons from December 1997 to March 2000, have shown wind direction in the upper atmosphere may affect thunderstorm development. During the middle of the rainy season clouds over the Amazon often behave as if they were over the open tropical oceans. He said, "Typically with an easterly wind in the upper atmosphere, thunderstorms grow best vertically, have large updrafts and great amounts of lightning, as they typically do over land masses. While an upper level westerly wind causes them to develop characteristics of storms over oceans, where they have weaker vertical structures and weaker updrafts and less lightning." Zipser noted that convection should not be solely based on upper level wind direction.

Adler will present comprehensive 2-year tropical rainfall and anomaly maps that give scientists a better understanding of global patterns of distribution and intensity of rainfall. All of these findings may help shed light on the evolution of global weather and climate patterns which lead to droughts and floods.

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.

Information and images about the TRMM mission are available at: http://trmm.gsfc.nasa.gov/.