La Niña occurs when the water is cool across the equatorial Pacific Ocean. Its opposite is El Niño, which is when water is warm across the equatorial region of the Pacific Ocean. This is important because La Niña and El Niño can affect tropical weather conditions, including the formation of tropical systems. In addition, La Niña can lead to less rainfall along the coasts of South and North America.
In the image to the right, we can see where cool water (shown in blue), stretches across the equatorial region of the Pacific Ocean. However, it is not uniform. There are pockets of warm water interspersed with this cooler water.
Acquired by the Ocean Surface Topography Mission/Jason-2 satellite, this map shows a 10-day average of sea-surface height centered on September 6, 2010. Because water expands with rising temperatures, satellites can use sea-surface height as a proxy for temperature. Areas where the water surface is higher (and therefore warmer) than average are shades of red-brown, and areas where the water surface is lower (cooler) than average are blue. Normal conditions appear in white.
via : La Nina in progress
