La Niña
La Niña is a significant climate phenomenon characterized by cooler-than-average sea surface temperatures in the central and eastern Pacific Ocean, which occur when stronger-than-usual eastward trade winds push cold water from the depths to the surface. It is one part of the broader El Niño-Southern Oscillation (ENSO) cycle, which also includes El Niño, where warmer ocean temperatures prevail. La Niña events can last from nine to twelve months, although some have extended for several years, influencing global weather patterns across various regions.
The effects of La Niña on weather can be quite profound, often leading to increased rainfall and cooler temperatures in the northwestern United States, while causing warmer and drier conditions in the southeast. It also tends to enhance hurricane activity in the Atlantic and can lead to drought in southern regions of South America. While La Niña events occur less frequently than El Niño events, they typically last longer and have significant impacts, including notable cases from 1998 to 2001 and from 2020 to 2023. The ongoing research into the effects of global warming on the ENSO cycle continues to evolve, as scientists seek to understand the complexities of these atmospheric interactions and their wide-ranging consequences.
Subject Terms
La Niña
Definition
Two large weather anomalies alternate south of an equatorial band across the middle and eastern portions of the Pacific Ocean. One is El Niño, characterized by warmer-than-average surface waters; the other is La Niña, marked by cooler surface temperatures (the two are collectively designated as the El Niño-Southern Oscillation, or ENSO). is defined as Pacific surface temperatures of 0.5° Celsius or more below average for a period of at least five months. The cooling occurs as stronger-than-usual eastward trade winds blow across the Pacific, churning cold water from the ocean depths to the surface.
The Spanish names of these weather events originate from the appearance of El Niño off the coast of Peru at Christmastime; niño (boy child) refers to the birth of Jesus. The opposite pattern is termed niña (girl child), although at one time it was called El Viejo (the old man). ENSO does not occur on a scheduled basis but does happen regularly with vehement, widespread consequences.
Significance for Climate Change
The effects of global warming on ENSO, the causes of which are only incompletely known, remain the subject of scientific debate, particularly because so great a number of variables affect ENSO. To obtain more data and understand long-term weather patterns, a monitoring system in the Pacific collects data from buoys, satellites, and computer models. Hotter or colder surface Pacific waters alter overhead trade winds, thereby shifting the North American jet stream. Altering the track and strength of the jet stream produces exceptional rain or drought. The cold, heavy air from La Niña pushes the jet stream to the upper part of the United States.
On average, a La Niña event may last from nine to twelve months, appearing at the end of one year and extending into the next. Consequently, in the southeastern portions of the United States, winter temperatures are warmer and dryer than normal. In northwestern regions, they are cooler and wetter. Hurricanes in the Atlantic and tornadoes in the United States tend to increase in number and force during La Niña events. In South America, dryer-than-usual conditions prevail in southern regions.
El Niño events occur more frequently than do La Niña events, in a ratio of approximately two to one. However, La Niña events last longer. One such event lasted, with a brief interlude, from mid-1998 to early 2001. Another occurred during the latter half of 2007 through the first half of 2008, provoking epic rainfall in Australia and record snowfalls in parts of China. A La Niña occurred from 2010 to 2012. One of the strongest on record, it caused heavy rain that led to flooding. A rare three-year La Niña occurred in 2020 and lasted until 2023. It led to record-setting tropical cyclones in the Atlantic Ocean. Another La Niña occurred in June 2023 and lasted until January 2024. It was one of the strongest on record.
Bibliography
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D’Aleo, J. S., and P. G. Grube. El Niño and La Niña. Westport: ORYX, 2002. Print.
Di Liberto, Tom. "ENSO + Climate Change = Headache." Climate.gov. NOAA, 11 Sept. 2014. Web. 24 Mar. 2015.
Glantz, M. H. Currents of Change: Impacts of El Niño and La Niña on Climate and Society. 2nd ed. New York: Cambridge UP, 2001. Print.
"La Niña." National Geographic Education. Natl. Geographic Soc., 1996–2015. Web. 24 Mar. 2015.
"Revising La Niña and Winter Snowfall, NOAA, 24 Oct. 2024, www.climate.gov/news-features/blogs/enso/revisiting-la-nina-and-winter-snowfall. Accessed 17 Dec. 2024.
"What Is La Niña?" NOAA Pacific Marine Environmental Laboratory, www.pmel.noaa.gov/elnino/what-is-la-nina. Accessed 17 Dec. 2024.