What Progress Has Been Made In Predicting Significant Changes In Seasonal To Interannual Variability?
TOGA Program Completed: Enhanced Fundamental Knowledge Of The Ocean Contributing To Forecasting Ability, Including Anomalies In Temperature And Precipitation In The U.S. The Tropical Ocean-Global Atmosphere (TOGA) program, one of the first projects under the USGCRP, was successfully completed in 1995. A ten-year international research effort, TOGA produced fundamental new knowledge of the processes that couple the tropical Pacific Ocean to the global atmosphere and ultimately led to a successful prediction capability of the El Niño phenomenon. The program developed and implemented a tropical Pacific Observing System to monitor the state of the tropical Pacific Ocean, providing real-time records of the evolution of El Niño events. The centerpiece of this observing system is the Tropical Atmosphere Ocean (TAO) array, which is comprised of 68 moored buoys spanning the tropical Pacific measuring sea surface temperature, surface winds, and upper ocean thermal structure. TOGA also conducted an unprecedented international field campaign (TOGA COARE) in 1992-93 to quantify air-sea interaction processes in the tropical western Pacific Ocean. The data set resulting from the experiment is being analyzed to improve the understanding of the coupling between the ocean and the atmosphere and the representation of such coupling in models. TOGA developed a number of coupled ocean-atmosphere models, one of which successfully forecasted the El Niño of 1986-87 and 1991-92 more than a year in advance. Another model successfully predicted the continuance of El Niño conditions in 1992-93. Finally, individual TOGA researchers began distributing experimental forecast products to a number of tropical countries (e.g., Brazil and Peru), where they have been successfully used by government officials and farmers to sustain agricultural productivity.
Reference: Proceedings of the International TOGA Conference, WMO/ WCRP Report, Melbourne, Australia, April 2-7, 1995, Vol. 1 and 2, in press, 1995.
USGCRP Scientists Extend The Predictive Skill Of El Niño Forecasts A team of oceanographers and meteorologists have recently extended the useful lead-time predictive skill of El Niño forecasts. A coupled ocean-atmosphere data assimilation procedure yields substantially improved retrospective forecasts of El Niño for the 1970s and 1980s compared with previous forecasting procedures. The improvement is attributed to the explicit consideration of low frequency characteristics of air-sea interaction in the initialization of the model forecast. The results suggest that El Niño is more predictable than previously estimated. The assimilation of surface wind observations as part of the initialization process also eliminates the "spring barrier" to ENSO prediction, implying that it may not be intrinsic to the real climate system.
Reference: An Improved Procedure for El Niño Forecasting, Chen, D., et al., Science, submitted, 1995.
New Modeling Method Developed To Provide Global Forecasts A new two-tiered approach has been developed and tested for global climate forecasting. The method first uses a coupled ocean-atmosphere model to predict tropical Pacific sea-surface temperatures There are then used to force a high-resolution atmospheric model that provides climate forecasts out to two seasons. Prediction of seven large climatic events of the 1970s to 1990s by this technique are in general agreement with observations over many regions of the globe. The demonstrated forecast skill suggests that the approach can provide highly useful predictions of climatic anomalies associated with ENSO events during the northern winter of at least six months. The success of the method relies on the prediction and occurrence of significant warm or cold events that occur every two to four years; it is these events that tend to have the largest societal impact.
References: (1) A Two-Tiered Approach to Long Range Climate Forecasting, Bengtsson, L., et al., Science, Vol. 261, pp. 1026-1029, 1993; (2) Forecasting Global ENSO-Related Climate Anomalies, Barnett, T. P., et al., Tellus, Vol. 46A, pp. 381-397, 1994; (3) Experimental Predictions of Climatic Variability for Lead Time of Twelve Months, Hunt, B. G., et al., International Journal of Climate, Vol. 14, pp. 507-526, 1994.
First Multi-Seasonal Climate Forecasts Issued For U.S. With funding from the USGCRP, the Federal Government in January 1995 began issuing on a monthly basis the first-ever long-lead forecasts of seasonal mean temperature and precipitation for the United States. The forecasts are made for periods beginning one-half month after the forecast time, progressing by monthly increments to one year into the future. This capability is based on advances made through USGCRP research efforts leading to improved observing systems for the ocean and atmosphere, improved physical understanding of tropical ocean-atmosphere interactions, and significant gains in skill of climate models. This new product, which replaces the previous zero-lead one-season forecast issued during the past decade, extends the forecast period substantially out to one year and bases the forecasts on a blend of statistical and physical coupled ocean-atmosphere circulation models. One of the newest products of the USGCRP, the forecasts demonstrate the effectiveness in identifying and transferring "cutting edge" technologies from theory to applications as well as the importance of partnership and cooperation between the academic and government research communities.
References: (1) Long-Lead Seasonal Forecasts-Where Do We Stand?, Barnston, Anthony G., et al., Bulletin of the American Meteorological Society, Vol. 75, pp. 2097-2113, 1994; (2) The Long-Lead Multi-Season Climate Outlook, Climate Prediction Center, Vol. 1, No. 1, 1995.