August 2, 2001
Japan Marine Science & Technology Center
Reading the signs of El Ni_o occurrence
Observation of large-scale movement of warm water in the western equatorial Pacific Ocean with TRITON buoys
JAMSTEC (President: Takuya Hirano) observed a very strong eastward ocean current exceeding 1.5m/sec (5.5km/h) between the end of June and early July from data provided by TRITON observation buoys deployed off the coastal waters of Papua New Guinea. This indicates a large-scale movement of warm water to the east, and is thought to be a sign of an El Ni_o occurrence (Fig.1).
JAMSTEC reported the accumulation of warm water in the western equatorial Pacific in June last year. It is conjectured that El Ni_o occurs when strong westerly winds push a warm pool that has accumulated in the western Pacific to the east. Since last November JAMSTEC has observed on several occasions a movement of warm water to the east due to the effect of westerly winds. The current at that time was quite fast, which continued a month. It is therefore believed there is a high possibility that it may develop into El Ni_o.
JAMSTEC is deploying TRITON buoys in collaboration with TAO array program by the National Oceanic and Atmospheric Administration/Pacific Marine Environmental Laboratory (PMEL) to monitor the entire tropical Pacific Ocean.
The data obtained by TRITON and TAO buoys are integrated, then released by JAMSTEC and PMEL over the internet in semi-real time.
For further details, contact:
Yoshifumi. Kuroda, Associate Scientist
Ocean Observation and Research Department, JAMSTEC
XXXiΌOj. Shimura, XXXXXi^Cgj or XXXiΌOj. Tsukioka, XXXXXi^Cgj
Administration Department, Public Relations Division, JAMSTEC
JAMSTEC TRITON Buoy website: http://www. jamstec.go.jp/jamstec/TRITON/
Summary of TRITON buoy observation results
It is known that the ocean-atmosphere interaction in the warm pool in the western tropical Pacific Ocean affects the global atmosphere, and gives rise to the El Ni_o phenomenon every several years (Fig.2). JAMSTEC is deploying TRITON buoys (Fig.3) to observe water temperature, salinity, surface heat and rainfall and to discover the process which forms the warm pool.
Under the TRITON program, JAMSTEC is monitoring the El Ni_o phenomenon throughout the entire Tropical Pacific in collaboration with the TAO (Tropical Atmosphere Ocean) program by the U.S. National Oceanic and Atmospheric Administration/Pacific Marine Environmental Laboratory (PMEL). The TRITON buoy network is playing a key role as a part of the El Ni_o observation system in CLIVAR (Climate Variability and Predictability) International research program. It is also making an important contribution to the GOOS (Global Ocean Observing System) program for establishing a ocean observation network in the worldfs oceans.
2. Observation results
(1) Indicator for warm water movement: Water temperature distribution around the equator and depth of the 20C isotherm
In mid July the equatorial seawater temperature area extended from the western to the central Pacific Ocean, and surface water temperature of 29C was distributed beyond the dateline (Fig.4 top). Warm water accumulated in the eastward current was observed at 156E, and was 2C higher than average at a depth of 150m (Fig.4 bottom). By the end of July, this warm water had moved east to 140W (Fig.5 bottom), and it is thought that this will push up sea surface temperature in the eastern Pacific.
The 20C isotherm represents the thermocline, and is an indicator of how much heat is accumulated. The deeper the 20C isotherm, the greater the amount of warm water accumulated. JAMSTEC is looking carefully at data obtained from TAO/TRITON buoys along the equator showing the current (July 14, 2001) depth of the 20C isotherm and its anomaly from the average (Fig.6). The 20C isotherm is at a depth of around 170m near the dateline on the equator (Fig.6 top), which is about 10m deeper than climatological data (Fig.6 bottom). This indicates the warm pool is on the move from the western to the eastern Pacific Ocean. With westerly winds blowing on the western side and easterly winds blowing on the eastern side, the warm water was converged. This indicates the strong coupling between the atmosphere and the ocean.
3. Explanation of figures
Figure 1: Current speeds in north-south and east-west direction at 156E and 147E at a depth of 10m on the equator
On June 30, the buoy recorded a strong eastward current of the maximum of 1.5m/s at 156E on the equator. Similar variations were also recorded at 147E on the equator.
Figure 2: Concept of the phenomenon
Warm water is currently moving from the western to the eastern Pacific Ocean
Figure 3: TRITON buoy array
Figure 4: Water temperature distribution along the equator (top); anomaly from the climatological data (bottom) (July 14)
This shows 2C higher than the climatological data at a depth of 150m near the dateline in the central Pacific Ocean.
Figure 5: Water temperature distribution along the equator (top); anomaly from the climatological data (bottom) (July 29)
The warm pool continues to move eastward after July 14 into the eastern Pacific Ocean.
Figure 6: Depth of the 20C isotherm along the equator (top); anomaly from the climatological data (bottom)
The 20C isotherm is 10m deeper than the climatologic data near the dateline, indicating that the warm pool is currently moving eastward. We can see the winds that sweep into this warm pool, with an easterly blowing on the eastern side and a westerly blowing on the western side.