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| La Niña (meteorology) | |
|---|---|
| Name | La Niña |
| Period | Irregular, 2–7 years |
| Effects | Altered tropical Pacific convection, strengthened Walker circulation, ENSO phase |
La Niña (meteorology) is a climate phenomenon characterized by unusually cold ocean temperatures in the central and eastern equatorial Pacific that influences global atmospheric circulation. It represents one phase of the El Niño–Southern Oscillation alongside El Niño and interacts with coupled systems such as the Pacific Decadal Oscillation, the Madden–Julian Oscillation, and the Interdecadal Pacific Oscillation. Major meteorological agencies including the National Oceanic and Atmospheric Administration, the Australian Bureau of Meteorology, and the European Centre for Medium-Range Weather Forecasts monitor La Niña because of its strong influence on seasonal climate and hazard risk.
La Niña emerges as a cooling anomaly in the tropical Pacific that alters the Walker circulation and trade winds, modulating convection and precipitation patterns across the tropics and extratropics. Operational definitions and indices used by the World Meteorological Organization, the Joint Typhoon Warning Center, and the Climate Prediction Center include sea surface temperature indices such as the Niño 3.4, Niño 3, and Niño 4 regions and atmospheric metrics like the Southern Oscillation Index.
La Niña arises from coupled ocean–atmosphere feedbacks driven by strengthened easterly trade winds, which enhance upwelling of cold subsurface waters along the South American coast and increase westward surface currents. The Bjerknes feedback, first described in conceptual work related to the Bjerknes Prize tradition and the research of Jacob Bjerknes, links sea surface temperature gradients, zonal wind stress, and thermocline tilt in the equatorial Pacific. Subsurface processes such as equatorial Kelvin and Rossby waves, along with recharge–discharge mechanisms, are modulated by stochastic atmospheric forcing from phenomena like the Madden–Julian Oscillation and tropical cyclone activity monitored by agencies including the Japan Meteorological Agency and the Philippine Atmospheric, Geophysical and Astronomical Services Administration.
During La Niña, atmospheric teleconnections influence midlatitude jet streams and storm tracks, producing characteristic patterns across continents monitored by the European Centre for Medium-Range Weather Forecasts, the National Aeronautics and Space Administration, and the Intergovernmental Panel on Climate Change. La Niña tends to enhance tropical cyclone activity in the Atlantic Ocean basin while suppressing cyclone formation in parts of the Central Pacific, affecting forecasts issued by the National Hurricane Center and the Central Pacific Hurricane Center. Impacts also extend to polar regions where sea ice and circulation anomalies interact with patterns tracked by the National Snow and Ice Data Center and the Arctic Council.
La Niña produces regionally specific seasonal anomalies: increased rainfall and flood risk in Australia and parts of Southeast Asia as reported by the Bureau of Meteorology, drier conditions and drought in the American Southwest and parts of Peru, and colder winters in portions of the Northern United States and Canada through Pacific North American teleconnections. The phenomenon often modulates monsoon variability affecting the Indian Meteorological Department forecasts for the Indian subcontinent, influences the East Asian summer monsoon with implications for agencies like the China Meteorological Administration, and affects agricultural zones across Brazil, Mexico, and South Africa.
Operational ENSO prediction systems developed at institutions such as the National Oceanic and Atmospheric Administration, NASA, the Met Office, and academic centers like Scripps Institution of Oceanography use coupled general circulation models, empirically based statistical models, and multi-model ensembles to forecast La Niña onset and decay. Observing networks including the TAO/TRITON array, Argo floats, satellite missions by NOAA and ESA, and buoy lines maintained by regional centers provide real-time sea surface temperature, subsurface temperature, and wind measurements that feed into assimilation systems and seasonal outlooks issued by the World Meteorological Organization and national agencies.
La Niña influences food security, water resources, energy demand, and disaster risk management across nations such as Australia, Indonesia, United States, and Kenya by altering crop yields, hydropower generation, and wildfire risk; these impacts are assessed by organizations like the Food and Agriculture Organization and the United Nations Office for Disaster Risk Reduction. Insurance markets, emergency services, and supply chains managed by entities including the World Bank and multinational corporations factor ENSO-linked risk into resilience planning, while conservation programs run by institutions such as the International Union for Conservation of Nature consider biodiversity impacts in ecosystems from the Amazon Rainforest to the Great Barrier Reef.
Instrumental records document notable La Niña episodes such as the strong events in 1988–1989, 1998–2001, and 2010–2012, which were associated with floods, droughts, and shifts in tropical cyclone activity analyzed in studies by universities like Columbia University and University of California, San Diego. Paleoclimate proxies including coral records, tree rings, and sediment cores compiled by research programs at institutions such as the Paleoclimate Modelling Intercomparison Project and preserved in archives curated by the National Centers for Environmental Information extend the La Niña record into past centuries and millennia, revealing variability influenced by phenomena such as the Little Ice Age and long-term modes like the Pacific Decadal Oscillation.
Category:Climate phenomena