tifically, the engagement of the challenges in the Pacific proved so fruitful that once these were addressed, the TOGA community maintained its enthusiasm as oceanographic, atmospheric, and coupled-system problems were attacked. Funding and support were always only barely adequate, so focusing the resources on a limited area of the Pacific became a necessity.
TOGA's limited resources were focused on studying interannual variability in the tropical Pacific associated with ENSO. Consequently, other problems of importance, either ones known at the beginning of TOGA or issues that were identified during the program, remained unexplored. Although the focus on ENSO was consistent with the initial U.S. plan for TOGA (NRC 1983), the program did not cover the broader initial objectives for the international program (WCRP 1985), which were agreed on by U.S. scientists (NRC 1986).
It is well known from empirical studies that the global impacts of ENSO are strongly controlled by the annual cycle, and, in fact, can be thought of as modulations of the mean annual cycle. The very concept of anomalies requires the annual cycle to be known. While the climatology for sea surface temperature is well characterized, the climatologies of other basic quantities in the tropical Pacific—thermocline depth, surface currents, subsurface currents, and subsurface temperature—are still largely unknown, and will be determined only through many years of measurements. Furthermore, the annual cycle itself has components that result from strong coupling among ocean, atmosphere, and land processes. The skill of predictions of sea surface temperature in the tropical Pacific has proven to be strongly dependent on which seasons lie between the time at which and the time for which a prediction is made. Hence, further study is needed on the nature of the annual cycle and its strong variations around the globe, the impact of the annual cycle on interannual variability, and the predictability of interactions between the annual cycle and interannual variations.
Even the nature of ENSO, the basic interannual variability in the tropical Pacific, was not completely determined by TOGA. A ten-year program simply was not long enough to define the nature of ENSO's interannual variability. The nature of interannual variability outside the tropical Pacific remains also underexplored. For example, interannual variability of the strength and onset of the Asian monsoon and the midlatitude connections to ENSO present many unsolved problems. Much remains unknown about seasonal-to-interannual variability induced by midlatitude interactions on large scales between the atmosphere and oceans; induced by the interactions of the atmosphere with sea ice, snow, and land; and induced by the high-frequency forcing by the atmos