Of babies, oscillations, and guns

The eastern Pacific Ocean, from which North America's major weather patterns arise, swings from periods of warmer than average surface temperatures to periods when temperatures are lower than average. The extremes bring on the weather patterns called El Niño (warmer ocean waters) and La Niña (colder waters).

The warm phase got its name in 1892, when Peruvian geographers heard that coastal fishermen sometimes encountered unusually warm ocean currents near Christmas. El Niño is the baby Jesus.

By the 1920s, a parallel cold cycle was recognized, and the two components (warm and cold) were termed the "Southern Oscillation." La Niña (the baby girl) is a neologism coined in recent years to stand for "anti- El Niño" conditions.

We're supposed to be in a La Niña phase of colder sea temperatures this winter. Historically, Las Niñas bring dry conditions to southern California and the southwest U.S. (Los Niños bring wet weather.)

So, why all the rain if we're under the sway of a dry La Niña?

Something unusual is happening in the northern Pacific. A persistent high pressure area is sending storm tracks that would normally run parallel with the Washington/Oregon border much further south. (Something equally unusual - and oddly similar - afflicted Ireland and Britain this weekend. A persistent high over the north Atlantic sent Arctic weather south to spoil the plans of European travelers with record snowfalls.)

Will it keep on raining in L.A.? Kevin Trenberth, who heads the Climate Analysis Section at the National Center for Atmospheric Research, doesn't think so. He believes the north Pacific high will collapse and La Niña will prevail. Ocean temperatures are nearly four degrees (F) below normal, he says. A steep drop in temperatures is a strong predictor of a dryer-than-usual winter for L.A.

Oh . . . and about the guns. In the late 19th and early 20th century, Peru was a major exporter of seabird guano - essentially concentrated nitrate. Processed by big chemical companies in Europe, the guano became the high explosives that killed millions in World War I. The quantity and quality of Peruvian guano depended on what the seabirds ate. The supply of fish off the coast of Peru fluctuated with the cycles of El Niño and La Niña. More fish, more guano, more bang.

From fish to bird to artillery shell, brought by the babies of Christmas.

The image on this page was taken by flickr user Hellebardius. It is used under a Creative Commons License.

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