La Niña
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La Niña is a coupled ocean-atmosphere phenomenon similar to El Niño. During a period of La Niña, the sea surface temperature across the equatorial Eastern Central Pacific Ocean will be lower than normal by 0.5 °C. In the United States, an episode of La Niña is defined as a period of at least 5 months of La Niña conditions. The name La Niña originates from Spanish, meaning "the little girl", analogous to El Niño meaning "the little boy".
La Niña is the opposite of El Niño, where the latter corresponds instead to a higher sea surface temperature by a deviation of at least 0.5 °C. El Niño is famous due to its potentially catastrophic impact on the weather along both the Chilean and Australian coasts. Furthermore, La Niña is often preceded by a strong El Niño.
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[edit] Effects of La Niña
La Niña causes mostly the opposite effects of El Niño, for example, El Niño would cause a dry period in the Midwestern U.S., while La Niña would typically cause a wet period in this area.
[edit] Recent occurrences
There was a strong La Niña episode during 1988-1989. La Niña also formed in 1995, and in 1999-2000. The last La Niña was a minor one, and occurred 2000-2001. There last was a moderate La Niña, which developed in mid 2007. NOAA confirmed that a moderate La Niña developed in their November El Niño/Southern Oscillation Diagnostic Discussion, and that it would likely continue into 2008. According to NOAA, "Expected La Niña impacts during November – January include a continuation of above-average precipitation over Indonesia and below-average precipitation over the central equatorial Pacific. For the contiguous United States, potential impacts include above average precipitation in the Northern Rockies, Northern California, and in southern and eastern regions of the Pacific Northwest. Below-average precipitation is expected across the southern tier, particularly in the southwestern and southeastern states. [1]
However, El Nino conditions returned in June/July 2009, and may strengthen and last into 2010. The effects of El Nino in 2009 were already being seen in the fall of 2009 as the remnants of Tropical Storm Ida strengthened into a powerful coastal storm.[2] [3]
[edit] See also
- El Niño-Southern Oscillation (Main article on El Niño and the related Southern Oscillation, discussing the relation between these two and La Nina)
- Walker circulation
- Reproduction
