Niño 1+2

Niño 1+2
Name	Niño 1+2
Region	Eastern Equatorial Pacific
Coordinates	0°–10°S, 90°–80°W
Related	El Niño–Southern Oscillation, Niño 3, Niño 3.4, Niño 4

Niño 1+2 is a commonly used label for the easternmost sea surface temperature (SST) anomaly region in the equatorial Pacific, bounded roughly between the coasts of Peru and the Galápagos Islands and used in studies of El Niño–Southern Oscillation and tropical climate variability. The region is central to analyses by institutions such as the National Oceanic and Atmospheric Administration, the International Research Institute for Climate and Society, and the Japan Meteorological Agency, and it is frequently referenced in operational forecasts, historical reconstructions, and fisheries assessments by organizations like the Food and Agriculture Organization.

Definition and Characteristics

Niño 1+2 denotes SST anomalies in a box located off the coast of Peru and Ecuador adjacent to the Equator, characterized by shallow thermocline depths, intense upwelling, and strong air–sea coupling that modulates the southern Humboldt Current and coastal climate. Scientists at the Scripps Institution of Oceanography, the Woods Hole Oceanographic Institution, and the Plymouth Marine Laboratory emphasize its role in coastal warming episodes, while research groups at the IPCC, the WMO, and the Met Office examine its interactions with basin-scale modes such as the Pacific Decadal Oscillation and the Madden–Julian Oscillation. Historical episodes observed by expeditions aboard ships of the United States Exploring Expedition, data archives of the International Comprehensive Ocean-Atmosphere Data Set, and reconstructions from the Paleoclimate Modelling Intercomparison Project illustrate Niño 1+2's sharp seasonal variability and influence on regional climate.

Measurement and Indices

Indices for Niño 1+2 are calculated from SST grids produced by products like the Reynolds SST, the HadISST dataset, and satellite retrievals from platforms such as NOAA-AVHRR, ERS-2, and MODIS. Operational centers including NOAA/NCEI, ECMWF, and the Bureau of Meteorology compute anomaly time series relative to climatologies defined by the World Meteorological Organization baseline periods, and researchers apply statistical techniques from groups like the National Center for Atmospheric Research and the Lamont–Doherty Earth Observatory to derive indices that feed into indices such as the Oceanic Niño Index and the Multivariate ENSO Index. Paleoclimate proxies employed by teams at the Lamont-Doherty Earth Observatory, the University of Bremen, and the Swiss Federal Institute of Technology augment instrumental SSTs for long-term analyses.

Climatic and Oceanographic Drivers

Air–sea interactions involving Walker circulation anomalies, equatorial zonal winds measured by TAO/TRITON moorings, and thermocline fluctuations observed by ARGO floats drive variability in the Niño 1+2 box; these processes are also studied in coupled models developed at GFDL, UK Met Office Hadley Centre, and ECMWF. Coastal upwelling controlled by wind stress curl near the Peruvian Current and wind bursts associated with the Southern Oscillation and the Madden–Julian Oscillation modulate SSTs, while teleconnections to the Indian Ocean Dipole and the Atlantic Niño can influence eastern Pacific conditions, as demonstrated in studies published by researchers at CSIRO, NOAA/PMEL, and the Max Planck Institute for Meteorology.

Historical Variability and Trends

Instrumental records and reconstructions from the 20th century reveal strong interannual events such as the El Niño of 1982–83 and the El Niño of 1997–98 that produced pronounced warm anomalies in the easternmost Pacific, with contributions analyzed by investigators at Columbia University, Princeton University, and Stanford University. Long-term analyses by the IPCC and climate model ensembles from projects like the Coupled Model Intercomparison Project indicate shifts in the frequency and amplitude of eastern Pacific warming that are debated among teams at the University of California, Santa Cruz, National Taiwan University, and the University of Washington. Paleoclimate evidence from coral records collected near the Galápagos Islands, studies by the Smithsonian Tropical Research Institute, and sedimentary archives investigated by the National Oceanography Centre provide context for preindustrial variability.

Impacts on Regional Weather and Fisheries

Anomalies in the Niño 1+2 region strongly affect coastal precipitation, sea level, and marine ecosystems, with documented socioeconomic consequences for countries such as Peru, Ecuador, and Chile through impacts on artisanal and industrial fisheries targeting anchoveta and related stocks monitored by the Peruvian Navy, the Instituto del Mar del Perú, and the International Whaling Commission. Extreme warm events alter stratification and oxygenation with effects studied by teams at the Scripps Institution of Oceanography, the Universidad San Marcos, and the Universidad del Pacífico, and they influence regional weather patterns considered in reports by the World Bank, Inter-American Development Bank, and the United Nations Development Programme.

Monitoring and Prediction

Operational monitoring of Niño 1+2 relies on integrated observing systems such as ARGO, TAO/TRITON, satellite altimetry from TOPEX/Poseidon and Jason-3, and SST analyses from NOAA and the European Space Agency. Forecasts are produced by coupled prediction systems at NCEP, ECMWF, and the Met Office that assimilate data via methods developed at NOAA/GFDL, IRI, and the Japanese Agency for Marine-Earth Science and Technology. Seasonal outlooks used by agencies like the Food and Agriculture Organization and disaster managers at PAHO deploy model outputs from multi-model ensembles including the North American Multi-Model Ensemble and the APCC regional products.

Relationship to ENSO and Other Niño Regions

Niño 1+2 is one of several zonal SST regions (others include Niño 3, Niño 3.4, and Niño 4) used to characterize phases of El Niño and La Niña within the broader El Niño–Southern Oscillation framework analyzed by groups such as the Intergovernmental Panel on Climate Change and the World Climate Research Programme. While Niño 3.4 is often used for global teleconnection diagnostics in studies from NOAA, NASA, and NCAR, Niño 1+2 emphasizes coastal eastern Pacific processes critical to regional impacts examined by researchers at CSIC, CICESE, and the Universidad de Chile. Interactions among these regions are investigated in modeling centers like GFDL, UK Met Office, and ECMWF to improve understanding of differing "canonical" and "Modoki" event structures described in the literature by teams at Tohoku University, Pusan National University, and University of Tokyo.

Category:Pacific Ocean