February 1, 2007

Tropical Water Cycle Studied

U.S. scientists say they've determined rain evaporation and continental convection play an important part in the tropical water cycle.

The researchers, led by John Worden at the National Aeronautics and Space Administration's Jet Propulsion Laboratory, analyzed global measurements of the isotopic composition of water vapor from NASA's Tropospheric Emission Spectrometer to determine the processes driving the tropical hydrological cycle.

The scientists say they discovered rainfall evaporation significantly replenishes the humidity of the lower troposphere with up to 50 percent of rainfall being evaporated near convective clouds. Over tropical continents, however, the scientists say the isotopic signature of water vapor differs significantly from that of rainfall, suggesting the dominant moisture sources are convection of vapor from oceanic sources and evapotranspiration -- a combination of evaporation and plant transpiration.

The researchers said their findings provide unprecedented new information about hydrological processes that are critical for understanding the global climate system.

The study is detailed in the current issue of the journal Nature.