The Tropical Atmosphere Ocean (TAO) Array World Wide Web Site

The TAO array consists of nearly 70 moored buoys spanning the width of the equatorial Pacific Ocean (Figure 1), a distance over one third the circumference of the globe. Moorings of the array measure oceanographic and surface meteorological variables critical for improved detection, understanding, and prediction of seasonal-to-interannual climate variations in the tropics, most notably those related to the El Niño-Southern Oscillation (ENSO) events.

Figure 1: TAO Array

The development and implementation of a real-time ocean observing system in the tropical oceans was one objective of the recently completed 10 year (1985-1994) international Tropical Ocean Global Atmosphere (TOGA) program. The need for an ocean observing system in the Pacific was dramatized in the early planning stages for TOGA by the occurrence of the very strong 1982-1983 ENSO warm event, which was neither predicted nor even detected until nearly at its peak. The TAO array is now one of the cornerstones of this observing system which also includes drifting buoy arrays, a volunteer observing ship expendable bathythermograph network, island and coastal tide gauges, an island wind profiler network, and remotely sensed measurements from both operational and research satellites. The TAO project is a multi-national effort involving the participation of the United States, Japan, Korea, Taiwan, and France.

TAO measurements consist primarily of surface winds, sea surface temperature, upper ocean temperature and currents, air temperature, and relative humidity. Data from most sensors are telemetered to shore in real-time via Service Argos. A subset of these data are placed on the Global Telecommunications System (GTS) for distribution to operational centers for assimilation into weather and forecast models (Figure 2).

Data are received daily at NOAA's Pacific Marine Environmental Laboratory (PMEL) via Service Argos' Automated Distribution Service, where they are processed and quality controlled.

From the early stages of TAO development, it was recognized that data from the array needed to be accessible in near real-time to the entire oceanographic and meteorological community. The first TAO web pages, real-time data displays, and ASCII data file access via forms and pulldown menus were available in 1994. Technical information on TAO moorings, sensor characteristics, and sampling schemes have been added to the pages along with online articles, ENSO references, and other sources of available data. The TAO data delivery page provides access to daily averaged data up through the previous day, as well as access to higher resolution data that are available after a mooring is recovered. The TAO data display pages provide clear and detailed displays of the data selected by the user. Automated scripts are used to update the data files and displays nightly. In addition to data delivery and display, the TAO project has developed the El Niño Theme Page to explain El Niño, the Southern Oscillation and related phenomena. During September and October 1997, the suite of TAO Web pages received over three million hits each month.

The value of the real-time TAO data stream for climate monitoring, analysis, and prediction has most recently been been highlighted by the development of the current ENSO warm event. This event evolved extremely rapidly during the first half of 1997 (Figure 3), and has reached a magnitude larger than that of any previous warm event in the past 100 years, including the 1982-83 El Niño. Data from the array have provided for a day-by-day description in real-time of changing climatic conditions across the entire equatorial Pacific basin. Also, the most accurate predictions of the current warm event were made using coupled ocean-atmosphere models that incorporated TAO wind, sst and subsurface temperature data into their initialization schemes.

Figure 3: Five-day mean zonal wind, STT and 20°C isotherm depth, 2°S to 2°N average

A number of challenges were faced in setting up the TAO web pages. Due to the real-time nature of the data, all of the TAO data files and graphics which are dependent on them must be updated daily. Despite increasingly powerful central processors, several hours of computer time each day are required for reformatting, gridding, graphics display, and copying updates to the Web server. Standard HTML (V3.2) is employed in the TAO pages to guarantee access to users from any of the widely available Web browsers. CGI scripts have been written to create the gif images, and to return the gifs and any data requested to the user's web browser. Due to bandwidth limitations, a cache system has been implemented for gif files on the PMEL server. After a particular gif is generated from the data in response to the first user request on a given day, users making subsequent requests on the same day will receive the cached gif, saving cpu time on the server, and reducing response times for the user.

In the future, the TAO data set is expected to continue to grow in size and complexity with the integration of new sensors into the data stream, necessitating software and hardware enhancements on the TAO server. The implementation of Java Applets will enhance the degree of interactivity with users and will give them more control of the displays and data processing. Future efforts will concentrate on ensuring that high quality data, displays, and information are available to all interested users.