July 20, 1998 Research scientists using data from the recently launched Tropical Rainfall Measuring Mission (TRMM) satellite, a joint U.S/Japanese mission, are shedding new light on the phenomenon known as La Niña. TRMM research team members have successfully retrieved sea-surface temperature data from the TRMM Microwave Imager (TMI) instrument onboard the spacecraft.
This temperature data is giving scientists new insight into the complex evolution of the La Niña event -- the TMI is the only spaceborne microwave instrument observing sea-surface temperature in the tropics. The images show changes in sea-surface temperature, and ocean current movement and the dissipation of El Niño. While it is too early to draw definite conclusions, the results to date appear to confirm the onset of La Niña type conditions.
"TMI is an all-weather measuring instrument that can see through clouds," said Dr. David Adamec, oceanographer at the Goddard Space Flight Center, Greenbelt, MD. "The standard instrument (infrared radiometer), used to measure sea-surface temperature, must contend with clouds and atmospheric aerosols. Clouds block the flow of data, yet an uninterrupted consistent data stream is crucial for long-term climate study."
La Niña is essentially the opposite of the El Niño phenomenon and is characterized by unusually cold ocean temperatures in the equatorial Pacific, as compared to El Niño, where ocean temperatures are warmer than normal. La Niña and El Niño often are spoken of together and termed the El Niño/Southern Oscillations, or "ENSO." La Niña sometimes is referred to as the cold phase of the ENSO.
At the Earth's surface, La Niña effects on the world's climate tend to be opposite those of El Niño. At higher latitudes, El Niño and La Niña are just two of several factors that influence climate. However, the impacts of El Niño and La Niña at higher latitudes are most clearly seen in winter. During a typical La Niña year, winter temperatures are warmer than normal in the Southeast and cooler in the Northwest.
Knowledge of La Niña is not as mature as that for El Niño. For example, every strong El Niño is not necessarily followed by a La Niña. Scientists at Goddard are performing advanced studies of El Niño and La Niña through information obtained from satellites in space and instruments in the oceans.
Acquiring quality sea-surface temperature data via a microwave scanner has been a long-term aspiration among oceanographers for more than a decade, when the last microwave imager ceased operations. In addition, none of the previously existing microwave scanners had the capability of the TRMM Microwave Imager. Ideally, this information will be used for the improvement of weather forecasting, anomalous weather study, and a better understanding of ocean current alteration.
Several NASA missions study the effects of El Niño and La Niña with orbiting satellites. The joint U.S.-French TOPEX/Poseidon satellite measures sea surface height; the Sea- Viewing Wide Field-of-View Sensor (SeaWiFS) measures ocean color; and TRMM measures precipitation and sea-surface temperature. The Tropical Atmosphere-Ocean Array consists of nearly 70 moored buoys in the tropical Pacific designed by the National Oceanic and Atmospheric Administration (NOAA). The devices take real-time measurements of air temperature, relative humidity, surface winds, sea surface temperatures and subsurface temperatures down to a depth of 500 meters. Data from these moored buoys is processed by NOAA and then made available to scientists.
The TRMM Microwave Imager instrument was provided by NASA. TRMM was developed jointly by NASA and NASDA and launched last November from NASDA's Tanegashima Space Center, Japan.
This La Niña research 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.
Images on this research are available at URL: http://www.eorc.nasda.go.jp/TRMM
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