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Contents EXECUTIVE SUMMARY 1 1 OVERVIEW AND PRINCIPAL RECOMMENDATIONS 5 Terms of Reference, 5 TOGA Plans and Requirements for Observations, 6 Beyond TOGA: Ongoing Research on Short-Term Climate Variability and Prediction, 10 Principal Conclusions, 11 2 PANEL'S PURPOSE AND BACKGROUND 15 Terms of Reference, 15 Ocean-Atmosphere Observational System, 15 Appropriate Scales, 15 Observational Systems Required for Climate Prediction, 16 Development of Data Sets Required for the Use of Current and Anticipated Prediction Models, 17 3 THE PRINCIPAL OBSERVABLES 19 Order of Importance, 19 Surface Wind Stress, 21 Sea-Surface Temperature, 24 Upper-Ocean Thermal Structure, 27 xi
Executive Summary The task of the Panel on Near-Term Development of Operational Ocean Observations was to "develop a design for a global coupled ocean-atmo- sphere observational system required for climate prediction," specifically of interannual climate variations on the time and space scales that have been the focus of the Tropical Ocean and Global Atmosphere (TOGA) program (see Table 1 and Chapter 1, section "TOGA Plans and Requirements for Observations"). The intent was to build on the legacy of TOGA both in measurement systems and in the scientific rationale for them. We have carefully considered the successes of TOGA to date, and they are manifold. We have also taken stock of the work that remains to be done before a truly operational system for short-term climate prediction exists. We believe that to accomplish the next steps of that remaining work, as it relates to observations, the government agencies responsible for operational oceanic and atmospheric measurements, the agencies responsible for re- search programs in climate variability and prediction, and the scientific community interested in these problems all have important jobs to do. Spe- cifically: 1. Operational and research agencies must join forces to fund continu- ation of present TOGA observations beyond the formal end of TOGA in 1994. Ideally they should extend all TOGA observations, but we recognize the need for priorities. Details are given elsewhere in this report. The 1
2 OCEAN-ATMOSPHERE OBSERVATIONS highest-priority observing system for continuation is the TOGA Tropical Atmosphere Ocean (TAO) array in the Pacific. 2. Operational agencies, research agencies, and the scientific commu- nity must arrest and reverse the alarming international decline of surface and upper-air observations that are primarily provided by the World Weather Watch's meteorological network (stations and aircraft reports). Direct ob- servation of surface and upper-air wind, temperature, and humidity is a key element of the climate observing system as well as the basis for weather forecasting. 3. All three groups must initiate a deliberate expansion/extension of observations, starting with an Indian Ocean TAO array and increased cover- age of the tropical zone of this ocean with volunteer observing ships and drifters. 4. Scientists must develop ways to quantify the value of various obser- vations in terms of how much they improve climate predictions. As more is learned, the degree of impact on prediction becomes a more useful yard- stick, one that scientists and agencies should use to make inevitable rankings and selections of observations to build up and observations to winnow or cut back. Our actual ability to assess the impact on prediction is very rudimentary now. In the near term, such rankings and selections will have to be made on less quantitative grounds. Conservatism should be weighted heavily: do not disrupt or abandon long oceanographic or meteorological time series in the absence of clear evidence that they are redundant or are too imprecise to be useful for measuring climate variations. 5. To guide the necessary evolution of observing systems, the respon- sible agencies, whether operational or research, must incorporate ongoing, not one-time, close involvement of research scientists who use or make the observations in the planning, improvement, and modification of measure- ments. 6. When, as often happens, a set of observations begun under research funding is suggested for "transition" to an operational agency, both the research and operational sponsors must be clear that the receiving agency has a commitment to sustain the observations, the technical capability to do so successfully, and avenues for the ongoing involvement of scientists as noted above. What matters, ultimately, is the continuity of the measure- ments and the integrity of the time series. Satellite-based measurements have transformed our ability to observe and visualize global atmospheric and oceanic variability and will continue to do so. Satellite techniques can be applicable to many of the observables of concern in this report. In guiding the future use of satellite methods, two principles must be borne in mind:
EXECUTIVE SUMMARY 3 1. The measurements made by satellite sensors are usually only indi- rectly related to the geophysical parameter of interest. Temporal and spa- tial variability in atmospheric aerosols and water vapor and variability in sea-surface roughness not related to wind, for example, introduce errors and uncertainties into the satellite estimates of such oceanic parameters as sea- surface temperature, wind stress, and sea-surface elevation. Improvements to the algorithms that relate the satellite measurements to the parameters of interest must be pursued and the accuracy of the satellite measurements must be demonstrated before conventional observations are reduced or re- tired in favor of spacebome measurements. 2. Most satellite estimates will always require coincident direct-surface and upper-air measurements to perform the ongoing task of calibration, and surface platforms will be needed to make measurements not possible by remote sensing. The best determinations of the geophysical fields of inter- est will be obtained by combining satellite and direct measurements, blend- ing the unmatched spatial coverage of satellite sensors with direct observa- tions of greater accuracy or more direct coMection to the geophysical parameters of concern. Therefore, a well-chosen network of direct observations will become more, not less, important as satellite techniques advance.