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El Niño Returns This Winter

Global weather pattern to bring more rain to SoCal

khts_specialreport2

For all its stereotypical perfect weather and Hollywood glamour, the land of fruits and nuts can't seem to catch a break recently. What with the recession, budget crisis, and chronic wild fires, power shortages, and drought, it's been a rough year so far.

 

But amid all this, there is good news literally on the horizon: El Niño is back. Yes, it's going to rain for real this winter. Hopefully a good downpour or two will tamp down the fire danger. It will likely replace it with mudslides and flash flood warnings, but still, a nice change of pace.

 

According to John Makevich, Meteorology Instructor at COC, "there's still a lot of debate in terms of the sort of chicken-and-the-egg problem as to what causes what," but you can still be sure that "during El Niño conditions, Southern California can expect greater than normal rainfall."

 

The big storms are still some time off, though. Makevich says El Niño isn't expected to reach full swing until after the New Year. But I had to wear a jacket today, so as far as I'm concerned, winter is here and it's time to find out what puts the "ñ" in El Niño.

 

Under normal (non-El Niño) conditions, trade winds blow from east to west across the Pacific Ocean, pushing warm surface water westward to the tropical islands of the South Seas. As the warm water is moved out of the way, cold sub-surface water begins 'upwelling' near the coast of South America. The winds also fuel the cold Humboldt Current, which flows northward past Chile and Peru before turning out to the central Pacific.

 

"In an El Niño situation instead those trade winds actually calm down, so the warm water doesn't get pushed out towards the west as firmly, so what ends up happening is ... the warm water doesn't move away, it pretty much stays there. That's part of the reason the surface ocean temperatures are on the order of a degree warmer than they would normally be in the Eastern Pacific," says Mackevich.

 

During El Niño events, which occur every two to seven years, the weaker trade winds result in less upwelling of cold water, a weaker Humboldt Current, and different patterns of evaporation, condensation, and precipitation.

 

From here it gets a little complicated. Essentially, the warmer ocean temperatures change the locations of high and low pressure zones, ultimately bringing greater rainfall to the American southwest. Because seasons are reversed in the Southern Hemisphere, South America experiences a warm, wet summer at the same time Southern California experiences a rainy winter.

 

The official name for the effect is El Niño-Southern Oscillation. The Southern Oscillation is the sea-saw (get it?) of high pressure zones over the Pacific Ocean. High air pressure in the east means low pressure in the west, and vice versa. In the 1950's it was discovered that these fluctuations in pressure corresponded with the observed El Niño events, and were in fact part of the same phenomenon.

 

The phenomenon got its name when fishermen off the west coast of South America initially noticed unusually warm water which appeared near year's end. Because the phenomenon occurred around Christmas time, it was referred to as "El Niño," or "the boy child," referring to the infant Christ. La Niña, which describes the opposite effect - colder ocean temperatures and less rain for SoCal, is simply a contrary term. So when the weatherman says El Niño is here, you'll know just what, and who, he's talking about.