What Is La Niña: How It Affects The Climate

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What is La Niña?

The scientific definition of La Niña states that it is a natural climatic cycle, which takes place in the central and eastern tropical Pacific Ocean. It lasts three to six years, and in this period, temperatures which are cooler than normal sea-surface temperatures have an impact on global climate. La Niña is actually the cold part of a cyclic thermal oscillation in ocean surface temperatures, which takes place all over the tropical Pacific. La Niña, together with the warm section of the cycle El Niño, causes a variation of about 0.5 ºC from the normal ocean surface temperatures. The last time La Niña happened was from 1998-2000, and researchers say its effect on global weather will be felt again this year in the winter.

According to recent research and news from the US National Oceanic and Atmospheric Administration (NOAA), La Niña continued to increase in strength all during August. In all the latitudes examined by NOAA, the temperatures of the ocean surfaced cooled by 1.3-1.8 ºC. Climate models have given predictions that La Niña will last till early 2011 and in this winter, it will continue to cool further. This will have a profound effect on global weather. Since this climatic cycle has a long-lasting efect on the entire weather pattern of the world, it is very vital to understand what is La Niña and the subsequent changes it brings.

What La Niña Does To The Climate

The cooling of the ocean surface has an impact on tropical Pacific rainfall from Indonesia all the way down to South America. Certain areas, like northern Australia, have a wetter rainy season than expected with more than average rainfall. Among the variations which La Niña causes in the climate, there are alterations in the wind speed and direction. The Atlantic is downstream to the region affected by higher rainfall. La Niña decreases wind speed and direction throughout the atmosphere, and this increases the incidence of Atlantic hurricanes.

In the USA, La Niña usually causes drier than normal conditions in the Southwest starting in the late summer and continuing through the following winter. Drier than normal conditions also occur in the Central Plains during the fall and in the Southeast during winter. Also, La Niña winters are less cold than usual in the Southeast and colder than normal in the Northwest.

According to NOAA predictions, due to the abnormally high Atlantic Ocean water temperatures seen in the last 15 years, and wind patterns existing since 1995, (there have been weak easterly trade winds and high pressure in the upper atmosphere), 2010 may have a very strong hurricane season. NOAA has also predicted that La Niña will help in lowering global temperatures from the recently recorded high temperatures. The recorded terrestrial temperatures outside the tropical regions of the Northern Hemisphere were highest in July 2010. Furthermore, the global average over land in the last year was the second highest ever recorded. La Niña conditions have helped in counteracting these high temperatures all over the world.

Importance of La Niña’s World-wide Effects On Weather

What La Niña does to climate, environment, and global weather patterns is very important. Accurate predictions of La Niña’s world-wide effects are useful in planning disaster management for events like droughts, heavy rainfall, and hurricanes. For example, scientists are aware that the Pacific Northwest will be wetter than normal in the late autumn and early winter of La Niña years, and this will cause dry aquifers to fill up after dry spells. Accurate knowledge of what is La Niña and how it affects weather are vital in planning water management programs which help farmers in mitigating future loss.


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