Strong La Niña in December 2010

Peruvian fisherman named El Niño (Spanish for “the boy child”) after the Christ child because the climate phenomenon usually shows up around Christmas time. But its counterpart, La Niña, is the gift giver, bringing cold, nutrient-rich water to the equatorial Pacific off South America. Those nutrients are a boon to marine life, supporting a larger fish population and increasing the fishermen's catch. Fishermen might expect a good year ahead, as a strong La Niña is now dominating the Pacific Ocean.

“This is one of the strongest La Niña events in the past half century, and will likely persist into the northern hemisphere summer,” says Bill Patzert, an oceanographer and climatologist at NASA’s Jet Propulsion Laboratory. “Climatic impacts include heavy rains and flooding, which has damaged crops and flooded mines in Australia and Asia. It also has resulted in flooding in northern South America and drought conditions in Argentina. This powerful little lady is spreading her curses and blessings across the planet. She’s the real deal.”
 

Like El Niño, La Niña comes from changes in both the ocean and the atmosphere. High pressure usually dominates the atmosphere over the eastern Pacific, while low pressure tends to reign in the west. The pressure difference creates the trade winds, which blow surface water across the equatorial Pacific to a pool of warm water in the west. Cooler deep water wells up to replace the surface water. During La Niña events, the pressure difference and the resulting trade winds are stronger. The more intense winds push more water west, where it builds up north of Australia. Meanwhile, more cold water wells up in the central and eastern Pacific.

La Niña occurs only when both the ocean and the atmosphere change together, and in 2010, they have, says oceanographer David Adamec of NASA’s Goddard Space Flight Center. The unusual ocean temperatures and imbalance in air pressures alter weather patterns across the world.


“Weather effects are strong in the western Pacific,” says Adamec. “Australia is flooding in many areas.” La Niña rainfall patterns are also evident in the stark horseshoe-shaped region of unusually dry weather in the central Pacific.

La Niña typically affects weather patterns in North America beginning in January. “For ‘normal’ effects in the U.S., look for cold in the Upper Plains, dry and warm weather in California, dry weather in the southeast, especially Florida, and unusually soggy weather in the Northwest,“ says Adamec.

Because such a wide swath of the Pacific is cold, La Niña tends to keep a lid on global temperatures. 2010, however, was still shaping up to be the hottest year on record in spite of La Niña, according to scientists from NASA Goddard Institute for Space Studies.

1. References

2. Climate Prediction Center/NCEP. (2010, December 20). ENSO cycle: Recent evolution, current status and predictions. National Oceanic and Atmospheric Administration.
3. Hansen, J., Ruedy, R. Sato, M., and Lo, K. (2010, December 13). 2010—Global temperature and Europe’s frigid air. NASA Goddard Institute for Space Studies. Accessed December 23, 2010.
4. NASA Earth Observatory. (n.d.) La Niña. Accessed December 21, 2010.