June 20, 2000
Japan Marine Science and Technology Center
Observations by TRITON buoy array in the western euatorial Pacific Ocean
- Warm water accumulated at the largest scale for the past 10 years,
one of the conditions for causing El Nino.-
The Japan Marine Science and Technology Center (JAMSTEC) (President: Takuya Hirano) has monitored the entire Pacific Ocean in cooperation with the Pacific Marine Environment Laboratory (PMEL)/ U.S. National Oceanic and Atmospheric Administration (NOAA), to explicate the mechanism by which the El Nino is generated. Sets of TRITON buoys have been sequentially installed in the equatorial waters north of New Guinea since 1998. The observed data indicate that the largest warm water accumulated in the past 10 years has been formed in the western equatorial Pacific Ocean since March 2000. (See Fig. 1).
Next El Nino may occur in and after the spring of 2001, if strong westerly winds will continue to blow over the western equatorial Pacific Ocean during the comming winter and spring and pushing this warm pool east. The JAMSTEC will continue to carry out observation by TRITON buoy array, in order to collect wind and water temperature data.
Some of the results will be presented in the meeting of the Western Pacific Geophysical Meeting, the American Geophysical Union, which is to be held at the National Olympic Memorial Youth Center in Yoyogi, Tokyo from June 27 (Tuesday) to 30 (Friday) 2000.
The water temperature and meteorological data obtained by the TRITON buoys have been distributed in real time to worldwide meteorological organizations through the Global Telecommunication System (GTS) and used to daily weather forecast all over the world. In addition, the data collected by the TRITON buoys have been combined with those obtained by the PMEL's buoys, and disclosed from the JAMSTEC and PMEL home page to the public though the Internet.
Japan Marine Science and Technology Center
Kuroda and Ando, Ocean Research Department, Tel: 0468-67-3472
Taya and Kimura, Public Relations, Training and Education Division,
TRITON Home Page
Outline of observations obtained by TRITON buoy array
It is generally known that the atmosphere-ocean interaction in and around the warm pool formed in the tropical Pacific Ocean may have an impact on the global atmosphere to cause an El Nino phenomenon at intervals of several years. To explicate the mechanism by which the El Nino phenomenon is generated, an array of TRITON buoys was installed to observe the warm pool formation process, the water temperature and salinity distributions in the ocean, and the variations of heat and rainfall on the surface of the ocean with time. (See Fig. 2)
The TRITON Project (*1) has monitored the occurrence of any El Nino phenomenon over the entire tropical Pacific Ocean in conjunction with the TAO (Tropical Atmosphere Ocean) Project implemented by the Pacific Marine Environment Laboratory (PMEL)/ the U.S. National Oceanic and Atmospheric Administration (NOAA). The TAO buoy array installed west from the longitude of 156E have been gradually replaced with TRITON buoys since February 1990.
*1 : The TRITON Project forms a part of the El Nino observing system used under the internatinal reserach project CLIVAR (Climate Variability and Predictability) which is carried to predict climate changes, and plays an important role in developing this project. It also contributes to the GOOS (Global Ocean Observing System).
(1) Warm pool generation
The 20 deg-C isothermal line, representative of the surface thermocline (*2), is one of the indicators that show how much heat is accumulated in the surface layer. Seawater in the surface layer is warmer, as the isothermal line is at a greater depth. (See Fig. 1)
This study analyzed the warm pool formation process by using the 20 deg-C isotherm depth data obtained by the TAO/TRITON array installed along the equator as well as the time series data of deviations from the normal value. (See Fig. 3 "20 deg-C isotherm depth along the equator".) The results indicated that the 20 deg-C isotherm depth was as great as 210m on the equator, or the greatest since the buoys started to obtain the data in 1999.
*2 : This means the layer in which the water temperature drops more rapidly as the depth is greater.
(2) Comparison between the data in the year having the greatest El Nino in the history and those in the previous year
The 20 deg-C isotherm depth was about 10m greater in March to April 1996 than the average of 180m in the normal years. In the next years, 1997/1998, an El Nino phenomenon occurred. The 20deg-C isotherm depth was found further greater by about 30m in March to April 2000. It was then observed that the 20 deg-C isotherm depth were greater both in the south and north waters of the equator, and that the warm water was accumulated in the south and north waters larger than observed in 1996. (See Fig. 4 "Monthly mean 20deg-C isotherm depth at 156E.) Thus, the time series data collected by TRITON buoys suggested that after El Nino ended in May 1998, La Nina continued for about 2 years while sufficient heat was accumulated in the western tropical Pacific Ocean to provide a condition for causing the next El Nino.
3. Potebtial for the next El Nino
One of the conditions for causing El Nino is that strong westerly winds continue to blow over the warm water accumulated largely in the tropical western Pacific Ocean and pushes the warm pool east. Generally, this westerly winds are stronger associated with the monsoon in boreal winter, and weaker in summer.
There is enough potential that El Nino may occur in and after the spring of 2001, if a strong westerly winds continue to blow over the western tropicalPacific Ocean in the next winter and spring.
Therefore, it is important that observations will continue to be made by using TRITON buoy array in order to collect especially the wind and water temperature data in the western Pacific Ocean.