TAO

An El Niño nobody saw coming

The strong El Niño of 1982–83 developed in the tropical Pacific almost unobserved, and its effects were felt worldwide. The Tropical Ocean Global Atmosphere programme of the 1980s set up an array of moored buoys to watch the upper ocean and the winds along the equator. Construction began in 1985, led by NOAA's Pacific Marine Environmental Laboratory, and the full array of about 70 moorings was completed in 1994.

In January 2000 the array was renamed TAO/TRITON, after Japan's JAMSTEC replaced the moorings in the western Pacific with its own TRITON design.

What the moorings measure

Each mooring records wind speed and direction, air temperature, humidity, rainfall, sea-surface temperature and temperature at depth down to 500 metres, and sends the data by satellite to shore within hours, so that forecasters can use them. Salinity sensors were added to 55 moorings between 2006 and 2008.

The data go into the models that forecast El Niño and La Niña months ahead, and drive the seasonal forecasts of governments and insurers around the world.

A fragile service

The array depends on ships to service the buoys every year. In the early 2010s, a shortage of ship time degraded the array's data return, and the loss was felt in forecasts. It was later restored with extra funding and with additional types of buoys. The array is part of the Global Ocean Observing System and a model of a moored array that reports in real time.

A fragile success

The array's value was proved by its use in forecasts, and its fragility was proved by the interruption in the early 2010s, when ship time was cut and the number of working moorings fell sharply. Forecasters lost data from the central Pacific just as the models had come to rely on it. The response was a review that led to renewed funding and to new designs. Meanwhile, Argo floats and satellites provide partial cover of the same region, so that the observing system as a whole is more resilient than any one part. Redundancy across different technologies is a way to avoid single points of failure. The array also shows how a single research programme can become an operational service without a change of name: the same moorings serve scientists studying the ocean and forecasters issuing El Niño outlooks each month, and the funding and governance have to serve both.

Instruments and technologies

• ATLAS mooring A surface buoy with a tower of meteorological sensors and a mooring line carrying temperature and salinity sensors, anchored in 1,000 to 6,000 metres of water.
• Satellite telemetry Daily averages and hourly values sent by satellite to shore, to feed forecast models.
• Acoustic current meters Current profilers on some moorings measure the equatorial undercurrent.

Timeline

• 1985 Array construction begins, led by the PMEL TAO Project Office.
• 1994 Full array completed.
• 2000 Renamed TAO/TRITON in January.
• 2006 Salinity sensors begin to be added to 55 moorings (to 2008).

Key lessons for observation today

• A surprise can justify a network The unseen 1982–83 El Niño paid for the array. Observation gaps are exposed by events they fail to catch.
• Maintenance is part of the instrument Without ships to service them, buoys fail. Operations budgets are as important as capital.
• Real-time delivery changes use Data that reach forecasters in hours support operations, not only research. Telemetry design follows the use.

Sources

• NOAA PMEL, Global Tropical Moored Buoy Array: Pacific Ocean TAO
• Wikipedia, Tropical Atmosphere Ocean project
• NOAA Pacific Marine Environmental Laboratory