Abstract
This paper reviews the design of the Tropical Pacific Observing System (TPOS) and its governance and takes a forward look at prospective change. The initial findings of the TPOS 2020 Project embrace new strategic approaches and technologies in a user-driven design and the variable focus of the Framework for Ocean Observing. User requirements arise from climate prediction and research, climate change and the climate record, and coupled modeling and data assimilation more generally. Requirements include focus on the upper ocean and air-sea interactions, sampling of diurnal variations, finer spatial scales and emerging demands related to biogeochemistry and ecosystems. One aim is to sample a diversity of climatic regimes in addition to the equatorial zone. The status and outlook for meeting the requirements of the design are discussed. This is accomplished through integrated and complementary capabilities of networks, including satellites, moorings, profiling floats and autonomous vehicles. Emerging technologies and methods are also discussed. The outlook highlights a few new foci of the design: biogeochemistry and ecosystems, low-latitude western boundary currents and the eastern Pacific. Low latitude western boundary currents are conduits of tropical-subtropical interactions, supplying waters of mid to high latitude origin to the western equatorial Pacific and into the Indonesian Throughflow. They are an essential part of the recharge/discharge of equatorial warm water volume at interannual timescales and play crucial roles in climate variability on regional and global scales. The tropical eastern Pacific, where extreme El Nino events develop, requires tailored approaches owing to the complex of processes at work there involving coastal upwelling, and equatorial cold tongue dynamics, the oxygen minimum zone and the seasonal double Intertropical Convergence Zone. A pilot program building on existing networks is envisaged, complemented by a process study of the East Pacific ITCZ/warm pool/cold tongue/stratus coupled system. The sustainability of TPOS depends on effective and strong collaborative partnerships and governance arrangements. Revisiting regional mechanisms and engaging new partners in the context of a planned and systematic design will ensure a multi-purpose, multi-faceted integrated approach that is sustainable and responsive to changing needs.
Highlights
Sustained and systematic observation of the tropical Pacific Ocean has been a priority for nations around the basin since the 1980s, driven principally by the global climate effects of the El Niño/Southern Oscillation (ENSO), and by the demonstrated prediction skill based on ocean and air-sea interface observations
Fulldepth subsurface moorings have been deployed in the straits for periods of 1.5–3 years (Ganachaud et al, 2017); repeated glider transects across the southern entrance of the Sea have proven to be an adequate solution for providing estimates of coast-to-coast equatorward heat and freshwater transport to 1000 m, though transects can be aliased by eddies (Davis et al, 2012); Pressure Inverted Echo Sounders (PIES) and high density XBT transects have been combined with altimetry and Argo floats to infer the mass transport interannual variability through the Solomon Sea (Melet et al, 2010; Zilberman et al, 2013)
The Tropical Pacific Observing System (TPOS) 2020 process delineates the different steps of requirement assessment, from users through to the observing system itself
Summary
Sustained and systematic observation of the tropical Pacific Ocean has been a priority for nations around the basin since the 1980s, driven principally by the global climate effects of the El Niño/Southern Oscillation (ENSO), and by the demonstrated prediction skill based on ocean and air-sea interface observations. The central and eastern Pacific data returns were back to normal by 2015, but there are only two TRITON sites west of 165E Several studies suggest this degradation compromised our ability to monitor climate variability and to model and predict ENSO (Tollefson, 2014; Fujii et al, 2015, 2019; Chiodi and Harrison, 2017a,b; Xue et al, 2017). This challenging period should be seen in the context of a TPOS capability that had grown significantly over the last two decades and highlighted points of vulnerability that were not well understood or managed (Ando et al, 2017; Serra, 2018). Section “Eastern Pacific” discusses some of the eastern Pacific coastal aspects
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