Chapter 14 - Equatorial Processes

Chapter 14 Contents

14.4 Observing El Niño

The tropical and equatorial Pacific is a vast, remote area seldom visited by ships. To observe the region NOAA's Pacific Marine Environmental Laboratory has deployed a array of buoys to measure oceanographic and meteorological variables (Figure 14.14). The first buoy was successfully deployed in 1976 by David Halpern. Since that simple start, new moorings have been added to the array, new instruments have been added to the moorings, and the moorings have been improved. The program has now evolved into the Tropical Atmosphere Ocean TAO array of approximately 70 deep-ocean moorings spanning the equatorial Pacific Ocean between 8°N and 8°S from 95°W to 137°E.

Figure 14.14 Tropical Atmosphere Ocean tao array of moored buoys operated by the NOAA Pacific Marine Environmental Laboratory with help from Japan, Korea, Taiwan, and France.

The array began full operation in December 1994, and it continues to evolve. The work necessary to design and calibrate instruments, deploy moorings, and process data is coordinated through the TAO Project. It is a multi-national effort involving the participation of the United States, Japan, Korea, Taiwan, and France with a project office at the Pacific Marine Environmental Laboratory in Seattle, Washington.

The TAO moorings measure air temperature, relative humidity, surface wind velocity, sea-surface temperatures, and subsurface temperatures from 10 m down to 500 m. Five moorings located on the equator at 110°W, 140°W, 170°W, 165°E, and 147°E also carry upward-looking Acoustic Doppler Current Profilers ADCP to measure upper-ocean currents between 10m and 250m. The moorings are designed to last about a year, and moorings are recovered and replaced yearly. Data from the array are sent back through argos system, and data are processed and made available in near real time. All sensors are calibrated prior to deployment and after recovery.

Data from TAO are merged with altimeter data from Jasin and Envisat to obtain a more comprehensive measurement of El Niño. Jasin and Topex/Poseidon altimeter observations have been especially useful because they could be used to produce accurate maps of sea level every 10 days. The maps provided detailed views of the development of the 1997–1998 El Niño in near real time that were widely reproduced throughout the world. The observations (figure 10.6) show high sea level propagating from west to east, peaking in the eastern equatorial Pacific in November 1997. In addition, satellite data extended beyond the TAO data to include the entire tropical Pacific. This allowed oceanographers to look for extratropical influences on El Niño.

Rain rates are measured by NASA’s Tropical Rainfall Measuring Mission which was specially designed to observe rain rates. It was launched on 27 November 1997, and it carries five instruments: the first spaceborne precipitation radar, a five-frequency microwave radiometer, a visible and infrared scanner, a cloud and Earth radiant energy system, and a lightning imaging sensor. Working together, the instruments provide data necessary to produce monthly maps of tropical rainfall averaged over 500 km by 500 km areas with 15% accuracy. The grid is global between ± 35° latitude. In addition, the satellite data are used to measure latent heat released to the atmosphere by rain, thus providing continuous monitoring of heating of the atmosphere in the tropics.

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