New research shows that the accuracy of three-day rainfall forecasts in the tropics can be improved by as much as 100% percent by combining existing forecast models with satellite rainfall data. These findings were presented today at the annual American Meteorological Society's (AMS) meeting this week in Long Beach, Calif. These findings also will be featured in an upcoming edition of the Journal of Climate.
Researchers at Florida State University have found that by adding rainfall observations collected by NASA's Tropical Rainfall Measuring Mission (TRMM) satellite and other meteorological satellites to forecast models, they can more than triple the accuracy of rainfall forecasts for the first 12 hours of the forecast.
In addition, they found that using the past rainfall data collected from defense meteorological satellites and NASA's Tropical Rainfall Measuring Mission (TRMM) spacecraft could be used to increase the forecast skill 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 in the past. These model properties are then used to predict the rainfall for 3 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, Tallahassee, Fla. "Overall we're most interested in improving the three-day rainfall forecast skills. Our research has shown that the global, as well as the regional skills, using the multi-analysis superensemble, are higher with TRMM research data."
These forecast results are based on five experiments each during Aug. 1 to Aug. 5, 1998. The skill or 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 research data from the NASA TRMM spacecraft, scientists will more accurately, or with greater reliability, forecast rainfall in the tropics. This is particularly important when it comes to hurricane tracks and rainfall accumulations. Experimental forecasts made by this new technique during the '99 hurricane season, for instance, 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 affect human activities. "Making such improvements in even the short term forecasts", says Chris Kummerow, the TRMM project Scientist, "is important because it demonstrates that we are learning more about the behavior of rainfall within these models. Understanding rainfall patterns generated by our global climate models is an extremely difficult problem", he said. "Having additional information available from these weather forecast models has not only the obvious benefit of better short term forecasts, but may also help shed additional light upon the climate models.
In his paper, Krishnamurti highlights the various research methods used to come to these conclusions.
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 world-wide precipitation because so little of the planet is covered by ground-based radars. Presently, only two percent of the area covered by TRMM is covered by ground-based radars, said Dr. Christian Kummerow, TRMM Project Scientist at NASA's Goddard Space Flight Center, Greenbelt, Md..
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.
TRMM is a 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 from the TRMM mission are available on the Internet at URL: http://trmm.gsfc.nasa.gov/. More information on AMS is available at http://www.ametsoc.org/
David E. Steitz
Headquarters
Washington, DC
Phone: 202-358-1730
Allen Kenitzer
Goddard Space Flight Center
Greenbelt, Maryland
Phone: 301-286-2806
Stephanie Kenitzer
American Meteorological Society
Washington, DC
Phone: 562-628-8200