El Niño and La Niña
El Niño… People talk about it, but what’s the deal? What exactly is it? I must admit, I didn’t get the importance of it when I was at school. There simply wasn’t a lot of information about it at the time. Now we know more - although we still don’t really know the cause of El Niño events.
So, what is it? It is part of a major climate fluctuation, called the El Niño Southern Oscillation (ENSO). The other parts of this oscillation are La Niña, and neutral conditions.
Let’s start with neutral conditions. Trade winds blow westward across the Pacific Ocean. This causes warm surface water to be pushed together near Indonesia. The sea levels here are about 50 cm higher than across the Pacific in Ecuador! (Just as a side note, the sea surface is not a constant height globally.) The rising air in the west of the Pacific is warmed, and there is a good amount of rainfall. Over on the other side of the Pacific, nutrient-rich water rises up off the South American coast (to replace the water that was blown to the west). This upwelling supports marine ecosystems and fisheries.
However, with a cycle of about 3-7 years, the trade winds weaken. This leads to a rise in sea surface temperature in the east of the Pacific (around equatorial regions), and also a reduction of the upwelling previously mentioned. The warming of the central and eastern Pacific leads to a major shift in weather patterns across the Pacific region. The rain that previously fell over Indonesia and Australia instead falls over Peru. Australia and Indonesia go into drought conditions, whilst Peru gets heavy rainfall and flooding, as well as having fisheries adversely affected by the reduced upwelling. All this tended to start occurring around Christmas time, hence the name El Niño, “the boy”.
La Niña (“the girl”) is the opposite. The trade winds strengthen and the weather pattern is a more intense version of neutral conditions. Australia and Indonesia get flooding and South America gets drought.
So… That’s El Niño (and La Niña). And that’s more information than I got when I was at school!!! I hope it helps :)