SUMMARY

The Tropical Oceans and Global Atmosphere (TOGA) Program was designed:

  1. To gain a description of the tropical oceans and the global atmosphere as a time-dependent system, in order to determine the extent to which this system is predictable on time scales of months to years, and to understand the mechanisms and processes underlying that predictability;

  2. To study the feasibility of modeling the coupled ocean-atmosphere system for the purpose of predicting its variations on time scales of months to years; [and]

  3. To provide scientific background for designing an observing and data transmission system for operational prediction if this capability is demonstrated by the coupled ocean-atmosphere system.

These objectives were formulated because of the recognized scientific importance of natural variability in the climate system, the consequences of the variations for the economies and societies of the world, and the potential value of skillful predictions. The United States cooperated with the international community, as part of the World Climate Research Programme, to achieve these objectives. This document examines the extent to which the TOGA Program succeeded in meeting these objectives and the role of U.S. participation in the program. However, it has been difficult to determine which activities were part of, or initiated because of, TOGA. This difficulty reflects the ability of U.S. TOGA to leverage its resources by integrating its efforts with other national and international climate-research activities. This report takes an expansive view by considering almost all research on seasonal-to-interannual climate research from 1985 through 1994 to be associated with the international TOGA program.

TOGA largely fulfilled, and in some ways exceeded, its objectives. The program built and maintained the TOGA Observing System, which provided observations of E1 Niño and the Southern Oscillation (ENSO) in the previously poorly sampled region of the tropical Pacific. It developed coupled atmosphere-ocean models of the tropical Pacific Ocean, some of which now demonstrate skill in the prediction of tropical sea surface temperature months to a year or so in advance. TOGA spawned several process experiments, especially the Coupled Ocean-Atmosphere Response Experiment (COARE), which explored aspects of tropical atmosphere-ocean coupling that were poorly understood. As a result of these activities, a new capability for observing the surface and near-surface ocean and atmosphere in real time has been developed, a new depth of



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Learning to Predict Climate Variations Associated with El Niño and the Southern Oscillation: Accomplishments and Legacies of the TOGA Program SUMMARY The Tropical Oceans and Global Atmosphere (TOGA) Program was designed: To gain a description of the tropical oceans and the global atmosphere as a time-dependent system, in order to determine the extent to which this system is predictable on time scales of months to years, and to understand the mechanisms and processes underlying that predictability; To study the feasibility of modeling the coupled ocean-atmosphere system for the purpose of predicting its variations on time scales of months to years; [and] To provide scientific background for designing an observing and data transmission system for operational prediction if this capability is demonstrated by the coupled ocean-atmosphere system. These objectives were formulated because of the recognized scientific importance of natural variability in the climate system, the consequences of the variations for the economies and societies of the world, and the potential value of skillful predictions. The United States cooperated with the international community, as part of the World Climate Research Programme, to achieve these objectives. This document examines the extent to which the TOGA Program succeeded in meeting these objectives and the role of U.S. participation in the program. However, it has been difficult to determine which activities were part of, or initiated because of, TOGA. This difficulty reflects the ability of U.S. TOGA to leverage its resources by integrating its efforts with other national and international climate-research activities. This report takes an expansive view by considering almost all research on seasonal-to-interannual climate research from 1985 through 1994 to be associated with the international TOGA program. TOGA largely fulfilled, and in some ways exceeded, its objectives. The program built and maintained the TOGA Observing System, which provided observations of E1 Niño and the Southern Oscillation (ENSO) in the previously poorly sampled region of the tropical Pacific. It developed coupled atmosphere-ocean models of the tropical Pacific Ocean, some of which now demonstrate skill in the prediction of tropical sea surface temperature months to a year or so in advance. TOGA spawned several process experiments, especially the Coupled Ocean-Atmosphere Response Experiment (COARE), which explored aspects of tropical atmosphere-ocean coupling that were poorly understood. As a result of these activities, a new capability for observing the surface and near-surface ocean and atmosphere in real time has been developed, a new depth of

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Learning to Predict Climate Variations Associated with El Niño and the Southern Oscillation: Accomplishments and Legacies of the TOGA Program understanding of ENSO has been achieved, theoretical models for the mechanism of ENSO have been proposed, and the beginning of an understanding of the relationship between tropical sea-surface-temperature perturbations and the atmospheric response in the middle latitudes has been attained. However, TOGA failed to meet its objectives fully. The program did not live up to its name by completing studies throughout the tropical oceans and the global atmosphere, but instead concentrated only on the large signal of seasonal-to-interannual coupled atmosphere-ocean interactions in the tropical Pacific (the ENSO phenomenon). Variability and predictability arising from processes in other ocean basins, and from the interactions of the atmosphere with land and with ice, received scant attention. Understanding of the effects of tropical sea surface temperatures on the higher latitudes developed slowly. The program did not address the possibility of variability and predictability on seasonal-to-interannual time scales arising from interactions within the middle latitudes. Research on seasonal-to-interannual variations of atmospheric circulation conducted under other auspices was not well integrated with the TOGA Program. Implementation of both the COARE field program, the largest process study in TOGA, and the Tropical Atmosphere/Ocean (TAO) array, the heart of the TOGA Observing System in the tropical Pacific region, were both accomplished only near the end of TOGA, so that their usefulness for improving prediction could not be demonstrated within the time frame of the TOGA Program itself. The expected satellite-based observation system, especially a scatterometer for estimating surface winds, did not materialize. Observational strategies for understanding seasonal-to-interannual variability were not developed for anywhere but the tropical Pacific. These failures, combined with the unexpected difficulties in coupling complex atmosphere and ocean models, meant that while much progress was made, the full accomplishment of the TOGA objectives will be realized only by future programs. By developing short-term climate predictions (predicting tropical Pacific sea surface temperatures months to a year or so in advance), TOGA has transcended the confines of a research program. Climate prediction (and the applications of climate prediction) has become a motivation for limited-duration research programs, and will continue to demand attention far into the future. Tension developed during the second half of TOGA between research motivated by the ideal of operational prediction and actual operational prediction efforts. Incipient applications of climate predictions were initiated under TOGA and a prototype International Research Institute for Climate Prediction was designed. Such an institute would support the needs of individual regions, through Regional Applications Centers. Peru, Brazil, and Australia are already finding applications of short-term climate predictions useful to their own economies and

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Learning to Predict Climate Variations Associated with El Niño and the Southern Oscillation: Accomplishments and Legacies of the TOGA Program societies. Applications for the United States will depend on the development of predictive skill at higher latitudes; such skill is still meager. The implementation of U.S. participation in TOGA was accomplished through the U.S. Global Change Research Program (USGCRP) and was aided by an unusual set of institutional arrangements. In the United States, the program was funded and administered from an interagency project office, and scientific advice was provided by the National Research Council (NRC) through its TOGA Panel. Internationally, the program was administered by the International TOGA Project Office, advised by the TOGA Scientific Steering Group, and resources were gathered by the Intergovernmental TOGA Board. These management arrangements grew organically, according to the needs of the program, and were largely responsible for its smooth functioning. The successful mix of science and applications demonstrated by TOGA can serve as a model for other components of the USGCRP. TOGA involved studies of both the atmosphere and the ocean, as well as their mutual interaction. The program therefore had major effects on practice and education in the atmospheric and oceanic sciences. Meteorologists and oceanographers worked together on a single problem, crossing the disciplinary and institutional barriers in universities and government. The real-time distribution of oceanographic data, coincident with the growth of the information superhighway, made data freely available in ways totally different from those previously possible. Applications of short-term climate prediction established a link between scientists and society, translating society's concern with crop planning, water management, fisheries, disaster planning, etc. into a focused scientific endeavor. Predictions of ENSO are not possible without observations to initialize prediction schemes in the region of the Pacific where ENSO is strongest. Research on ENSO also places a high priority in data from this region. It is essential to maintain what we already have, in particular, the upper-air observing network, satellite altimetry, and the upper-ocean and surface-meteorological measurements made in and over the ocean. Guidance provided in NRC 1994a remains relevant, and we paraphrase two of its recommendations here. The TOGA Observing System in the Pacific, especially the moorings that constitute the TAO array, should be continued because of its value for initializing and evaluating systems making predictions of seasonal-to-interannual climate variations. The components of the system should be maintained until a serious study of their impact on prediction reveals them to be of marginal value or until a more cost-effective technique is demonstrably ready to replace them. The prediction of short-term climate variations is a nascent field. There is much to be learned on how to provide and apply such predictions. The provision and application of seasonal-to-interannual forecasts will require forging

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Learning to Predict Climate Variations Associated with El Niño and the Southern Oscillation: Accomplishments and Legacies of the TOGA Program links between the climate research community and the communities of applied climatologists, social scientists, and users of climate information. TOGA has brought us to a time for the establishment of a prototype international institute for making predictions and demonstrating the applicability of these predictions, as previously recommended in NRC 1995b. TOGA concentrated on only the strongest climate variation on seasonal-to-interannual time scales, ENSO, and concentrated on ENSO only in a limited geographic region where the signal is strongest, the tropical Pacific. Much research is still required to develop skill for predicting short-term climate variations caused by other processes or in other places. Unless they coordinate their efforts, researchers are unlikely to develop this skill efficiently. National and international programs are needed for research on, and development of, the exploitation of predictability and the making of predictions of seasonal-to-interannual climate variations throughout the world. In particular, the World Climate Research Programme study CLIVAR (Study of Climate Variability and Predictability)/GOALS (WCRP 1995) and its U.S. contribution GOALS, proposed in reports from the NRC (1994b, 1995a), provide a path for furthering the accomplishments and building on the legacy of TOGA.