La Niña, the counterpart to El Niño, alters rainfall patterns over the Pacific and Indian Ocean basins. La Niña develops when stronger-than-average trade winds push the warm surface waters of the equatorial Pacific west. Since cold water rises to replace the warm water, La Niña leaves the eastern and central Pacific Ocean much cooler than normal, while the western Pacific is much warmer than normal. These anomalies in sea surface temperature are mirrored in rainfall patterns, with warmer-than-normal temperatures resulting in enhanced rainfall. In general, La Niña brings unusually heavy rain to the West Pacific, Indonesia, parts of Southeast Asia, and northern Australia.
This image shows the unusual rainfall pattern associated with La Niña. The image was made from the Multi-satellite Precipitation Analysis produced at NASA’s Goddard Space Flight Center, using rainfall measurements collected between December 19, 2007 and January 18, 2008. The image shows rainfall anomalies, or deviations from the average rainfall observed during the same period from 1998 through 2007. Regions that received more rain than average are blue, average rainfall is white, and below-average rainfall is brown. The rainfall pattern revealed by this image is typical of La Niña. A classic horseshoe pattern of above-average rainfall covers parts of the West Pacific, Indonesia and southern Southeast Asia, and northern Australia. A smaller horseshoe-shaped area of below-normal rainfall enfolds the region where ocean temperatures were cooler than average.
Superimposed on the La Niña pattern is the most recent Madden-Julian Oscillation (MJO). The Madden-Julian Oscillation is a large area of thunderstorms that moves slowly eastward from the Indian Ocean into the Pacific Ocean over a period of 30-60 days. In this image, the thunderstorms associated with the most recent Madden-Julian Oscillation were in the process of moving from Southeast Asia and Indonesia into the western Pacific. Since the cluster of thunderstorms had just left the Malaysian Peninsula, the area was unusually dry. In an average La Niña, the peninsula would also be wetter then normal. The Madden-Julian Oscillation was also contributing to the enhanced rainfall north and northeast of Australia. The unusually heavy rains shown in this image caused widespread flooding in northern Australia.
The Multi-satellite Precipitation Analysis used to make this image is based on data collected by the Tropical Rainfall Measuring Mission (TRMM) satellite. TRMM was launched into service with the primary mission of measuring rainfall from space. It can also be used to calibrate rainfall estimates from other sources. TRMM is a joint mission between NASA and the Japanese space agency, JAXA.
- Further Reading
- La Niña, a fact sheet available from NASA’s Earth Observatory.