Sampling for the backbone observing system has as its goal to:
- Observe and quantify the state of the ocean, on time scales from weekly to interannual/decadal
- Provide data in support of, and to validate and improve, forecasting systems
- Support calibration and validation of satellite measurements
- Advance understanding of the climate system in the tropical Pacific, including through the provision of observing system infrastructure for process studies
- Maintenance and, as appropriate, extension of the tropical Pacific climate record.
Depending on the mechanisms that are of importance, different spatial sampling strategies may be needed in different regions. Temporal and spatial resolution needs also depend upon the region and variable of interest; in and near the equatorial waveguide, higher temporal and meridional resolution of temperature, salinity, carbon system variables and currents are needed than in many extra-equatorial areas. Similar considerations probably apply to the near-surface layer and the eastern and western boundary regions. For some variables and in some regions, the scales that we wish to observe are well known; in others, it will be necessary to plan for an evolving sampling strategy as new information is gained.
In principle we wish to use an integrated approach; that is, the Backbone TPOS achieves its objectives through a combination of in situ and remote approaches, augmented as appropriate with models and data assimilation.
The initial “ENSO observing system” in the tropical Pacific depended upon a combination of repeat XBT tracks (some with ship-borne ADCPs), surface drifters, Voluntary Observing Ships, island tide gauges, the sparse TAO mooring array and some repeat hydrography; satellite oceanography was in its infancy at the beginning of this system. Considerable technological progress has been made since then. Satellite ocean observing is now an established technology: The Argo profiling float array is a proven source of temperature, salinity, and float displacement observations, and air-sea carbon flux observations are proven. New autonomous technologies such as gliders and wavegliders have been developed and also need to be considered in the future backbone TPOS observing strategy.
Consistent long-term climate records are fundamental to diagnose trends and multi-decadal variability, and to maintain credible climatologies. The GCOS Climate Monitoring Principles for the evolution of observing system elements comprise an important set of guidelines for the transition from the present into the TPOS beyond 2020. The TPOS 2020 Project provides an opportunity to evaluate options and to conduct any needed transitions in a way that minimises harm to the Tropical Pacific ocean data record.
The major objective of this Task Team is to articulate the purpose and requirements for the backbone observations in the tropical Pacific and to recommend a feasible process for achieving a new configuration of the observing suite.
Some specific questions that must be addressed are:
- What are the unique capabilities of the ‘legacy’ ENSO observing system elements, and what are the enhancements that have been made over the past decade that should be continued in the TPOS beyond 2020 in support of a backbone observing system? This consideration should include efficiency, effectiveness and utility.
- What contributions can we reasonably assume will continue courtesy of global observation efforts (eg, SST, altimetry, Argo, TAO/TRITON moorings, scatterometer winds, ocean colour)
- What enhancements/modifications to these efforts should be sought?
- What will be the data synthesis strategy for integrating the full multivariate suite of backbone observations into a coherent view of ocean structure and variability of the region?
- Anticipating the future evolution of prediction systems and drawing on advice from the Biogeochemical TT, determine the initial strategy for backbone biogeochemical observations?
These questions should be addressed while considering the feasibility of new observation platforms and sensors for the backbone sampling and what mitigation efforts/options are needed to ensure robustness of the observing system.
Consideration should also be given to the adequacy of data systems, taking into account the tight time constraints of operational assimilation systems.
The Task Team should liaise with the other Task Teams as appropriate and take account of guidance being developed on time-series.
 Work initiated at SC Meeting 1, including guidance on the approach.
 The US National Research Council (at the request of NOAA) provided a definition Climate Data Record in the context of satellite records: “a time series of measurements of sufficient length, consistency, and continuity to determine climate variability and change.” In TPOS, we might wish to use a more general interpretation for climate record that is not specific to time series:
“A climate record is (observed) evidence about climate, usually in some permanent form, with sufficient extent, quality, integrity and consistency to detect climate variability and change.”