The Tropical Atmosphere Ocean Array (TAO) for the 21st Century

The Tropical Atmosphere Ocean (TAO) Array has transitioned from the National Oceanic and Atmospheric Administration's (NOAA) research arm to its operational arm within the National Weather Service at the National Data Buoy Center (NDBC). NDBC's transition strategy had two motives: First, to maintain continuity of the existing observations for the climate record and, second (but equally as important) to ensure its future contributions and survival which will be accomplished by a comprehensive equipment upgrade, known as the TAO Technology Refresh (TAO Refresh).

The array consists of 55 surface ocean moorings and four subsurface moorings straddling the central and eastern equatorial Pacific Ocean making meteorological and ocean near-surface and subsurface observations. A few of the moorings have additional sensors for air-sea flux measurements. The Array's operational significance is for the improved detection, understanding, and prediction of the El Nino and Southern Oscillation (ENSO) phenomena, which in turn have significant implications for climate predictions. In addition, the observations are used for real-time operational numerical weather prediction and marine weather analysis. The moorings also serve as important and convenient platforms to perform various ocean and atmospheric research projects. TAO is one of the components of the Global Tropical Moored Buoy Network which is one of the subsystems of the Global Climate Observing System (GCOS) and the Global Ocean Observing System (GOOS), which is the oceanographic component of the Global Earth Observing System of Systems (GEOSS).

TAO grew out of the success of the Tropical Ocean, Global Atmosphere Project (TOGA) and was completed in 1994. NDBC assumed responsibility for data management of TAO in 2005 and the at-sea operations in 2007. TAO Refresh was always an important component of NDBC's transition of the Array. Presently, the Array uses the Next Generation Autonomous Temperature Line Acquisition System (ATLAS) mooring system, designed in the 1990s and the deployments completed in 2001, now termed TAO Legacy.

After exhaustive parallel testing proving the integrity and continuity of NDBC's implementation of TAO Legacy data management functions, NDBC assumed responsibility for TAO. NDBC applied its operational perspective to institute procedural changes to provide the TAO data with a wider scope and applicability than originally conceived by the research community. NDBC made more data available by releasing data from systems that became unmoored and drifted outside of the 2x 10-degree data grids for TAO. Now NDBC releases the data under standard drifting buoy identifiers to the operational weather and oceanographic communities. NDBC instituted public access to real-time status of the stations and their sensors, so that users can readily assess the health and utility of the data or lack of data for their applications.

NDBC proposed a technology refresh plan in 2006 to replace obsolete sensors and limited communications capabilities. To overcome limited real-time data availability from the polar orbiting satellites of the TAO Legacy, NDBC intends to transition to a commercial satellite system (Iridium), already proven within NDBC's coastal and offshore weather and oceanographic buoy systems, that will allow the Array to meet requirements for hourly resolution time series data and high-frequency weather phenomena, and at the same time keeping the power consumption low. NDBC designed a new, all-purpose data collection system that effectively interfaces between the new sensors and the new communications system. This new data collection system, usually called a data logger or payload, is also being used on NDBC's Coastal Weather Buoys (CWB). The new data collection and communications systems will allow NDBC to provide in real-time the comprehensive data that was normally only-available once the sensors are recovered every 12 months. NDBC determined that the most cost-effective approach for sensor replacement was to use commercial off-the-shelf sensors time-tested and proven in the Triangle Trans-Ocean Buoy Network (TRITON) Array developed and operated by the Japan Marine Science and Technology Center. Just like in the case above, where the payload is common with NDBC's other buoy systems, these commercial off-the-shelf oceans sensors are common with our CWB systems, as well. Sharing common technology between several systems is very efficient, cost effective, and contributes to the overall maintainability, reliability, and availability of each system. The new system will require updates to the data management system to handle the increase in real-time data, expanded measurements and quality control indicators, and their necessary metadata records.

As part of a comprehensive test plan to ensure continuity of the climate records, NDBC has conducted laboratory tests and has successfully deployed several prototype TAO Refresh systems in the Gulf of Mexico and the Pacific TAO array. Currently five TAO Refreshed buoys are deployed in the Pacific for in-situ testing with TAO Legacy. Initial evaluations indicate good agreement between TAO Legacy and TAO Refresh.

The Refreshed buoy will meet requirements for National Weather Service, climate research, and international GOOS/GCOS purposes while increasing the real-time data available for climate analysis, forecasts, and numerical model predictions. The climate research community has requested more salinity and ocean current sensors in the surface layer and upper thermocline and more complete surface flux capabilities and higher vertical resolution in the mixed layer for more moorings.

The paper will present the existing and planned capabilities for the Array and will present further results of the inter-comparisons between the two systems. It will also update the climate community on progress in fielding an operational TAO Array that can meet the rigorous demands of the climate and operational communities in the 21st century.