David E. Steitz

Headquarters, Washington, DC

(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)



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

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:


Information on the AMS is available at URL: