Precipitation Data: Understanding El Nino/La Nina

Cynthia M. O’Carroll

Cynthia.M.OCarroll.1@gsfc.nasa.gov

301-614-5563

RELEASE NO: 2000-

RESEARCHERS CREATE FIRST GLOBAL LONG-TERM PRECIPITATION DATA SET FOR UNDERSTANDING EL NINO/LA NINA

NASA scientists have completed the first globally complete long-term data set for use in understanding El Nino/La Nina events. The data set, part of the
Global Precipitation Climatology Project (GPCP), is a result of rainfall analysis that examines precipitation monthly around the globe over a 20-year period.

The GPCP Project Scientist, Dr. Robert Adler of NASA’s Goddard Space Flight Center, Greenbelt, Md., will present the analysis as part of a Global Change
Conference at the 80th American Meteorological Society Annual Meeting. The presentation will be held at 1:45 p.m. on Jan. 12, 2000, at the Long Beach
Convention Center, Long Beach, Calif.

This data is a result of combining information from a number of polar orbiting satellites, geosynchronous satellites and rain gauge information to give the best
analysis of global precipitation on a monthly time scale. The polar orbiting Defense Meteorological satellites carry the Special Sensor microwave/Images
instrument designed to estimate precipitation. The geosynchronous satellites are the Geosynchronous Operational Environment Satellites from the U.S., the
Meteosat from Europe and the Geosynchronous Meteorological Satellites from Japan. Data from NASA’s recently launched Tropical Rainfall Measuring
Mission spacecraft also is used to validate the global analyses.

According to Adler, these globally averaged values and the regional and time-varying patterns are extremely important as validation for computer models of the
global atmosphere. “Before we can use these models to successfully predict El Nino’s and other climate phenomena they must be able to reproduce these
observations,” stated Adler. ” With this information, we can better understand these phenomena and the critical regional precipitation variations associated with
them.”

The current analysis indicates La Ninas increase drought conditions over Borneo and New Guinea and precede an increase in sea surface temperature in the
central Pacific Ocean, which is tied to the large increase in rainfall there. These observations are not accurately reproduced in computer models, thus indicating
a need for significant model improvement.

A global map of El Nino/La Nina variations shows that during El Nino there is an increase of precipitation extending from the central Pacific, across the
southern U. S. and across the Atlantic to the European coast. A decrease in rainfall is observed during El Nino events in New Guinea southeastward across
the South Pacific all the way to the straits of Magellen between South America and Antarctica.

This new data set and the associated techniques developed by the GPCP provide a more complete and more accurate picture of these large-scale climate
variations. The results should spur both a better understanding of the phenomena and provide the observations that the models must reproduce in order to
advance the prediction of these events.

The GPCP is part of the World Climate Research Program, under the auspices of the United Nations World Meteorological Organization, which provides
guidance for international climate research. The GPCP is made up of atmospheric scientists from NASA, the National Oceanic and Atmospheric
Administration and other research institutions in the U.S., Europe and Japan.

To find out more about this project visit this web site:
http://rsd.gsfc.nasa.gov/912/gpcp/gpcp.html