David E. Steitz
Headquarters, Washington, DC                   January 12, 2000
(Phone:  202/358-1730)

Allen Kenitzer
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-2806)

Stephanie Kenitzer
American Meteorological Society, Washington, DC
(Phone:  562/628-8200)

RELEASE:  00-9

NASA SATELLITE GREATLY IMPROVES ACCURACY
OF TROPICAL RAINFALL FORECASTING

     New research shows that adding rainfall data from NASA's 
Tropical Rainfall Measuring Mission (TRMM) satellite and other 
meteorological satellites to forecast models can more than triple 
the accuracy of short-term rainfall forecasts. 

     These findings by researchers at Florida State University, 
Tallahassee, FL, were presented today at the annual American 
Meteorological Society's (AMS) meeting in Long Beach, CA, and will 
be featured in an upcoming edition of the Journal of Climate.  

     In addition, researchers found that using the rainfall data 
collected from defense meteorological satellites and TRMM can be 
used to increase the forecast accuracy even further.  Their method 
examines the behavior of a number of different forecast models and 
selects those properties from each model that lead to the true 
rainfall as observed by the TRMM satellite.  These model 
properties are then used to predict the rainfall for three days 
into the future, with remarkable success.

     "Including rainfall into the multi-forecast model, or 
'superensemble' model, is a unique approach," said Prof. T.N. 
Krishnamurti, the paper's lead author and a TRMM scientist at 
Florida State University.  "Overall we're most interested in 
improving the rainfall three-day forecast accuracy.  Our research 
has shown that the accuracy of global and regional forecasts using 
the superensemble is higher with TRMM research data."

     These forecast results are based on five experiments each 
conducted Aug. 1 to Aug. 5, 1998.  The forecast accuracy was 
higher over all tropical regions.  Scientists attribute this 
success to a combination of improved analyses available from the 
superensemble approach as well as the availability of accurate 
rainfall estimates over the tropics from the TRMM satellite.

     For years, scientists have attempted to improve the short-
term forecasts in the tropics, but only minor improvements were 
made.  Now, with the research data from the NASA spacecraft, 
scientists will more accurately forecast rainfall in the region.  
This is particularly important when it comes to hurricane tracks 
and rainfall accumulations.  Experimental forecasts made by this 
new technique during the 1999 hurricane season, for example, 
correctly forecast the track of major hurricanes such as Dennis 
and Floyd.

     Scientists have a keen interest in how potential changes in 
the global climate might affect the associated rainfall patterns 
as they in turn affect human activities.  "Making such 
improvements in even the short-term forecasts is important because 
it demonstrates that we are learning more about the behavior of 
rainfall within these models," said Chris Kummerow, the spacecraft 
project scientist at Goddard Space Flight Center, Greenbelt, MD. 
"Understanding rainfall patterns generated by our global climate 
models is an extremely difficult problem. Having additional 
information available from these weather forecast models has the 
obvious benefit of better short term forecasts, and may help shed 
additional light upon the climate models."

     TRMM is NASA's first mission dedicated to observing and 
understanding tropical rainfall and how it affects the global 
climate.  The TRMM spacecraft fills an enormous void in the 
ability to calculate worldwide precipitation because ground-based 
radars that measure precipitation cover so little of the planet.  
Ground-based radars cover only 2 percent of the area covered by 
TRMM, said Kummerow.

     TRMM has produced continuous data since December 1997.  
Tropical rainfall, which falls between 35 degrees north latitude 
and 35 degrees south latitude, comprises more than two-thirds of 
the rainfall on Earth.  Previous estimates of tropical 
precipitation were usually made on the basis of weather models and 
occasional inclusion of very sparse surface rain gauges and/or 
relatively few measurements from satellite sensors. The TRMM 
satellite allows these measurements to be made in a focused 
manner.

     TRMM, a NASA-Japanese mission, is 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 from the TRMM mission are available on the 
Internet at URL:

                  http://trmm.gsfc.nasa.gov/

     Information on the AMS is available at URL: 

                  http://www.ametsoc.org/

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