NASA Pinpoints Where Rain Comes From and Where It Goes

A new NASA computer model can now tell exactly where in the world rain or snow that provides local water originated. Scientists can use this "water vapor tracer" to improve rainfall and drought forecasts and gain a deeper understanding of climate change.

The model simulates water movement in the atmosphere around the world, and traces it from the places where it evaporates to the places where it falls back to Earth.

"If I see rain or snow in the central U.S., I can now tell you how much of the moisture came from the Gulf of Mexico, how much came from the tropical Atlantic Ocean and so on," said meteorologist Mike Bosilovich of NASA's Data Assimilation Office at Goddard. Bosilovich is lead author of the study being published in the March-April issue of the Journal of Hydrometeorology. "The model gives us a much clearer picture of how water moves in the atmosphere than we have ever had before."

By identifying water vapor movement in the atmosphere, weather forecasters will better understand how evaporation from a particular place contributes to local and regional precipitation, leading to more accurate weather forecasts. The model can actually pinpoint individual regional sources of atmospheric moisture, rather than combining them. Bosilovich said if scientists can understand how geographic sources of atmospheric moisture fluctuate from year to year, they also will have a clearer picture of how climate changes in the long term.

For the complete article on tracing rainfall, go to: http://www.gsfc.nasa.gov/news-release/releases/2002/h02-62.htm