La Niña
What is La Niña?
La Niña occurs when the trade winds strengthen and cause the “tongue” of cold water near the coast of South America to extend westward toward the central, tropical Pacific Ocean (picture). This brings more cold water to the region around the equatorial Pacific Ocean and causes changes in pressure as well. These pressure changes are such that low pressures are present west of the International Dateline and high pressures are east of the dateline (cold ocean surface temperatures are present east of the dateline).
La Niña also has affects globally, these can be seen on the map.
Although La Niñas do not happen as often as El Niño's, they are an important part in equalizing pressures and temperatures around the globe.