La Niña

La Niña (Spanish, girls ') is a weather event that usually occurs following an El Niño event. It's kind of its counterpart. La Niña goes with above-average air pressure differences between South America and Indonesia, accompanied (see Southern Oscillation ). This leads to stronger trade winds and a generally increased, but cooled Walker circulation. From the Passat, the warm water is driven to the surface to Southeast Asia in the Pacific Ocean. Off the coast of Peru about flows of cold water from the deep that lies to 3 ° C below the average temperature.

The generally increased, but now cooled, atmospheric circulation is the cause of teleconnections that affect the Atlantic, as these air masses reach by the West Wind Drift in the temperate latitudes of the Atlantic Ocean.

The effects are not as strong as with El Niño, La Niña, but still has a significant impact:

• In the western Pacific, the water at the surface is warmer. The result: The more different the temperatures in the eastern part of the Pacific Ocean from those in the western regions, the more rain falls on Australia's northeast coast.
• In Southeast Asia, La Niña brings torrential rain, which can trigger landslides. In the second half of 2010, it has never rained so much, since weather records are created. The record rains in late 2010 resulted in the northeastern Australian state of Queensland and northern New South Wales to flooding, the extent of which corresponded approximately to half the area of the German state of Bavaria - while in the south west of Australia, there was an extreme drought, as it had never been observed.
• In South America, however, it rains less and the deserts wither.
• In North America, the occurrence of hurricanes is favored.

In the direct area of ​​influence - if you let the teleconnections ignored - occur but less natural disasters as the El Niño.

... as well as here in November 2007 ...

And ... most recently in April 2008, where in addition an anomaly of the Pacific decadal oscillation ( PDO ) west of the North American coast can be seen.

It is striking that the number of La Niña events between 1970 and about 1995 removed and have increased the El Niño events. It therefore came up with the assumption that the anthropogenic greenhouse effect was responsible, but could not be proved that, especially since the late 1990s, the trend has been reversed and the long-time average of the 20th century is reached again (Source: SOI Archives of the Australian Bureau of Meteorology ). Currently, it is believed that these fluctuations are largely due to natural variations, as warm in the Pacific at intervals of about 20-30 years and cold phases, called Pacific decadal oscillation ( PDO ), with its two phases El Viejo and La Vieja, alternate. The short-term impact of global warming on such air distribution systems has been probably overestimated, which may, however, in a few years to change, because these systems have to changes of individual factors over a certain inertia.