Science Questions

What is El Niño?

Sun, 13th Feb 2011

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Question

Peter Rubinelli asked:

Hi Chris,

 

Thanks for the very excellent science podcast. I have a question. What is El Niño and does it affect the jet stream, and if so how?

 

Peter Rubinelli

West Lafayette, IN

USA

Answer

Diana -   El Niño is usually defined as having occurred when you get a high air surface pressure on top of the Pacific Ocean and the actual surface of the Pacific Ocean increases in temperature.  What happens as a result of this is you get the Humboldt current – that's the sort of nutrient-rich cold current of water - moving, and it moves away from the coast of South America.

That takes away all the nice happy fish, and it means that all the fishermen in South America lose a lot of their stock.  And it also causes quite heavy rain and flooding in the southern parts of America.  Conversely, you get droughts and sometimes even bush fires on the eastern side of the Pacific or where Australia is.  This kind of thing can happen roughly every five years on average.

But as for the jet stream, we don't really know for sure, but it looks like El Niño can pull the polar jet stream slightly further south, which means that north America can suffer maybe more rainfall, maybe a bit more snow, colder winters, but we don't really know if it actually affects Europe, possibly.

Dave -   Also, essentially you're changing the temperature of a great big area, a huge area, of the Pacific Ocean which will affect which area you're heating the air above, so it’ll change the kind of global circulation of air currents slightly, which will have all these knock-on effects.

Diana -   Exactly.  It’s a huge system and a hugely complex system as well and some people have even recorded maybe more droughts occurring in Africa during El Niño event, which is the other side of the world.

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Peter Rubinelli asked the Naked Scientists: Hi Chris,   Thanks for the very excellent science podcast. I have a question. What is El Nino and does it affect the jet stream, and if so how?   Peter Rubinelli West Lafayette, IN USA What do you think? Peter Rubinelli, Mon, 7th Feb 2011

El Niño are ocean currents characterized by warm equatorial surface temperatures on the Pacific Ocean.

La Niña are ocean currents characterized by cold equatorial surface temperatures on the Pacific Ocean.



Photos from NOAA:
http://www.elnino.noaa.gov/lanina.html

This is a natural oscillation that changes somewhere from about 6 months to a couple of years, and has a profound effect on global weather patterns and temperatures.  In part because the oceans are a large heat-sink.  If the surfaces of the oceans reflect cold water, then the planet will tend to cool.  If the ocean surfaces reflect warm water, then the planet will tend to experience warming, perhaps not significantly representing the actual temperatures of the oceanic heat sink.

For example, 1998 was one of the hottest years on record, and was a strong El Niño cycle.
It was followed in 1999&2000 by a strong La Niña cycle, with somewhat of a rebound in global temperatures.

There will be characteristic rainfall patterns, especially around the Pacific Ocean based on La Niña/El Niño patterns.

CliffordK, Mon, 7th Feb 2011

That's really very informative, I like this thread. aserniaL, Wed, 9th Mar 2011

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