The Tropical Pacific Observing System (TPOS) was designed during the highly successful Tropical Ocean Global Atmosphere (TOGA) experiment, which was completed in 1994 and revolutionized observational understanding of the tropical Pacific and El Niño–Southern Oscillation (ENSO) dynamics; it also set the tone for real-time data availability and routine seasonal forecasts. ENSO is the Earth’s dominant mode of climate variability on seasonal to interannual time scales, influencing temperature and precipitation across the globe. Measurements collected from the tropical Pacific region form the foundational capability for predictions of ENSO, providing advance warning for changes in weather patterns that influence droughts and water resources, wildfires, air quality, fisheries, and food security around the world.

TPOS 2020 was a focused, finite term project, beginning in 2014 and completing in 2020, with its primary outcome being an internationally-coordinated and supported sustainable observing system for the Tropical Pacific Ocean. TPOS 2020 set out to deliver a new integrated Tropical Pacific Observing System (TPOS) design that expands the array to cover a broader range of latitudes and oceanic and atmospheric regimes, improving coupled weather and subseasonal forecasting capabilities. The TPOS 2020 Project catalyzed the need for a new observing system design to take advantage of innovations in observing technologies and enable the next generation of earth system modeling.

TPOS 2020 operated with the following scientific objectives:

1. To redesign and refine the TPOS to observe ENSO and advance scientific understanding of its causes,
2. To determine the most efficient and effective observational solutions to support prediction systems for ocean, weather and climate services, and
3. To advance understanding of tropical Pacific physical and biogeochemical variability and predictability.

The TPOS 2020 Project worked to evaluate, and where necessary, change all elements that contribute to the Tropical Pacific Observing System based on a modern understanding of tropical Pacific science. The project aimed for enhanced effectiveness for all stakeholders, informed by the development and requirements of the operational prediction models that are primary users of TPOS data. TPOS 2020 embraced the integration of diverse sampling technologies, with a deliberate focus on robustness and sustainability, and will deliver a legacy of improved governance, coordination and supporting arrangements.

The Project worked within the Framework for Ocean Observing developed by the Global Ocean Observing System (GOOS) and used this as a reporting mechanism to other relevant coordination mechanisms. Further, the TPOS 2020 project welcomed partnerships with other global ocean observing communities, the meteorological community, and the operational centers that use TPOS data for ocean state estimates and forecast initialization, and coastal ocean communities.

TPOS 2020 aimed to deliver the following benefits:

1. A refreshed and more effective design for the TPOS, promoting sustainability, and making full use of new and emerging technologies
2. Greater cooperation and coordination among the international sponsors and contributors to the TPOS, delivering efficiency, reduced risk and greater robustness
   Facilitation of experiments and studies in process parameterisation and modelling to guide improvements in climate prediction and associated applications
3. Integration of biogeochemical and biological sampling into the TPOS design and implementation
4. Fuller assessment of climate change signatures and the impacts in the tropical Pacific

The Project facilitated and embraced observing element contributions from multiple agencies and countries through a coordinated portfolio of resources and high-level oversight of the scientific and technical design, sub-projects and interfaces to the user community.