La Niña
La Niña ( Spanish for 'the girl') is a weather event that usually occurs after an El Niño event. It is, so to speak, its counterpart. La Niña is associated with above-average differences in air pressure between South America and Indonesia (see Southern Oscillation ). This leads to stronger trade winds and a generally increased but cooled Walker circulation . The warm surface water of the Pacific is increasingly driven to Southeast Asia by the trade winds . As a result, more cold water flows in from the depths off the coast of Peru , which is up to 3 ° C below the average temperature.
The generally increased, but now cooled, atmospheric circulation is the cause of teleconnections that affect the Atlantic, because these air masses reach the Atlantic through the westerly wind drift in the temperate latitudes.
The effects are not as strong as the El Niño, but La Niña has a significant impact nonetheless:
- In the western Pacific, the surface water is warmer. As a result, the more the temperatures in the eastern part of the Pacific Ocean differ from those in the western areas, the more rain falls on the Australian northeast coast.
- In Southeast Asia, La Niña brings heavy rain that can trigger landslides. In the second half of 2010 it rained there more than ever since the weather records began. The record rains at the end of 2010 led to floods in the northeastern Australian state of Queensland and in northern New South Wales, the extent of which was roughly half the area of the German state of Bavaria - while in the southwest of Australia there was an extreme drought like it had never been observed before.
- In South America, however, it rains less and the deserts are drying up.
- In North America, the occurrence of hurricanes is favored.
In the area of direct influence - if the teleconnections are not taken into account - fewer natural disasters occur than in an El Niño.
The temperature of the sea surface from January to February 2006 clearly shows the cooling characteristic of La Niña in the equatorial Pacific ...
... just like here in November 2007 ...
... and as last in April 2008, where an anomaly of the Pacific Decade Oscillation (PDO) can also be seen west of the North American coast.
It is striking that the number of La Niña events decreased between 1970 and around 1995 and the El Niño events increased. It was therefore assumed that the anthropogenic greenhouse effect was responsible for this, but this could not be proven, especially since the trend has clearly reversed since the late 1990s and the long-term average of the 20th century has been reached again (source: SOI- Archives of the Australian Bureau of Meteorology). It is currently assumed that these fluctuations are largely due to natural fluctuations, since warm and cold phases in the Pacific occur at intervals of approx. 20-30 years, called the Pacific Decade Oscillation (PDO) with its two phases, El Viejo and La Vieja, take turns. The short-term influence of global warming on such climate distribution systems has probably been overestimated so far, but this may change in a few years, as these systems have a certain inertia in relation to changes in individual factors.
See also
Web links
- NOAA La Niña Page , page with many backgrounds on the La Niña phenomenon (English)
- NASA Earth Observatory: La Niña Fact Sheet , Explanation of the La Niña Phenomenon