ENSO has continued to propel much of the observational, modeling and theoretical progress of the past 30 years, but despite three decades of focused attention of the climate community, ENSO forecasting skill remains stubbornly slow to improve after the initial advances. In fact, while forecast skill for the full set of retrospective ENSO events has increased slightly, forecast skill for recent events has been lower than for the events prior to the turn of the century (Barnston et al., 2012). Coupled GCMs with far better resolution and more developed physical parameterizations than those of the 1980s have seen improvements in ENSO simulations (Wittenberg et al., 2006; Delworth et al., 2012), but have produced only modest progress in forecast skill (Davey et al., 2002; Turner et al., 2005). Strong hints of decadal or longer modulation of ENSO characteristics complicate the prediction problem, as have the emergence of what might be other “modes” of ENSO. These may be related to changes in the background state that alter the relation between upper ocean heat content and SST (McPhaden, 2012), or they may simply emerge at random from the stochastically-forced and/or chaotic ENSO system.

Credit: NOAA Climate.gov

The Tropical Pacific Observing System (TPOS) is designed to monitor and observe the tropical Pacific and to meet the experimental and operational needs of today and the future. Observations of the region are critical to support prediction systems for ocean, weather and climate services. Variability of this strongly coupled atmosphere-ocean system reverberates across the global climate and provides a principal source of interannual climate predictability extending worldwide.

The overwhelming lesson of the past three decades of ENSO observation is its diversity and the ongoing succession of surprises in the expression of these events. The potential for future surprises in ENSO behavior is high. It appears that the relatively easy issues of wave-carried ocean memory are largely solved, but further advancement will entail diagnosing and explaining the mechanisms of air-sea heat and momentum exchange, in both fluids, which is unlikely to be accomplished by model experiments alone. This situation demands continued attention by the sustained observing system to the physical processes involved in tropical ocean-atmosphere interaction.

The community has made remarkable progress in observing and understanding the tropical Pacific over the last several decades.

An abbreviated history of key events and achievements leading to the formation of TPOS.