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Sea surface temperature anomalies in November 2007, showing La Niña conditions

La Niña (/lɑːˈnnjə/, Spanish pronunciation: [la ˈniɲa]) is a coupled ocean-atmosphere phenomenon that is the colder counterpart of El Niño, as part of the broader El Niño–Southern Oscillation (ENSO) climate pattern. The name La Niña originates from Spanish, meaning "the little girl", by analogy to El Niño meaning "the little boy". In the past it was also called an anti-El Niño,[1] and El Viejo (meaning "the old man").[2]

During a La Niña period, the sea surface temperature across the eastern equatorial part of the central Pacific Ocean will be lower than normal by 3 to 5 °C (5.4 to 9 °F). An appearance of La Niña persists for at least five months. It has extensive effects on the weather across the globe, particularly in North America, even affecting the Atlantic and Pacific hurricane seasons, in which more tropical cyclones occur in the Atlantic basin due to low wind shear and warmer sea surface temperatures, while reducing tropical cyclogenesis in the Pacific Ocean.

Background

Observations of La Niña events since 1950, show that impacts associated with La Niña events depend on what season it is.[11] However, while certain events and impacts are expected to occur during events, it is not certain or guaranteed that they will occur.[11]

[11] However, while certain events and impacts are expected to occur during events, it is not certain or guaranteed that they will occur.[11]

Africa

La Niña results in wetter-than-normal conditions in Southern Africa from December to February, and drier-than-normal conditions over equatorial East Africa over the same period.[13]

Asia

During La Niña years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific Ocean, which increases the landfall threat in China.[14] In March 2008, La Niña caused a drop in sea surface temperatures over Southeast Asia by 2 °C (3.6 °F). It also caused heavy rains over Malaysia, the Philippines, and Indonesia.[15]

Australia

Across most of the continent, El Niño and La Niña have more impact on climate variability than any other factor. La Niña is characterized by increased rainfall and cloud cover, especially across the east and north; snow cover is increased.

There is a strong correlation between the streng

During La Niña years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific Ocean, which increases the landfall threat in China.[14] In March 2008, La Niña caused a drop in sea surface temperatures over Southeast Asia by 2 °C (3.6 °F). It also caused heavy rains over Malaysia, the Philippines, and Indonesia.[15]

Australia

[27] it involves temperature anomalies in the eastern Pacific. However, aside from differences in diagnostic criteria,[a] non-traditional La Niñas were observed in the last two decades, in which the usual place of the temperature anomaly (Niño 1 and 2) is not affected, but rather an anomaly arises in the central Pacific (Niño 3.4).[28] The phenomenon is called Central Pacific (CP) La Niña,[27] dateline La Niña (because the anomaly arises near the dateline), or La Niña "Modoki" ("Modoki" is Japanese for "alternate / meta / similar-but-different").[29][30] These "flavors" of ENSO are in addition to EP and CP types, leading some scientists argue that ENSO is a continuum of phenomena – often with hybrid types.[31]

The effects of the CP La Niña similarly contrast with the EP La Niña – it strongly tends to increase rainfall over northwestern Australia and northern Murray-Darling basin, rather than over the east as in a conventional La Niña.[30] Also, La Niña Modoki increases the frequency of cyclonic storms over Bay of Bengal, but decreases the occurrence of severe storms in the Indian Ocean overall, with the Arabian Sea becoming severely non-conducive to tropical cyclone formation.[32][33]

Recent years when La Niña Mod

The effects of the CP La Niña similarly contrast with the EP La Niña – it strongly tends to increase rainfall over northwestern Australia and northern Murray-Darling basin, rather than over the east as in a conventional La Niña.[30] Also, La Niña Modoki increases the frequency of cyclonic storms over Bay of Bengal, but decreases the occurrence of severe storms in the Indian Ocean overall, with the Arabian Sea becoming severely non-conducive to tropical cyclone formation.[32][33]

Recent years when La Niña Modoki events occurred include 1973–1974, 1975–1976, 1983–1984, 1988–1989, 1998–1999, 2000–2001, 2008–2009, 2010–2011, and 2016–2017.[29][34][35]

The recent discovery of ENSO Modoki has some scientists believing it to be linked to global warming.[36] However, comprehensive satellite data go back only to 1979. Generally, there is no scientific consensus on how or if climate change may affect ENSO.[37]

There is also a scientific debate on the very existence of this "new" ENSO. A number of studies dispute the reality of this statistical distinction or its increasing occurrence, or both, either arguing the reliable record is too short to detect such a distinction,[38][39] finding no distinction or trend using other statistical approaches,[40][41][42][43][44] or that other types should be distinguished, such as standard and extreme ENSO.[45][46]