That old, vaguely familiar weather buzzword has been floating around the media in sensationalized fashion for many of the months thus far in 2014: El Niño.
File photo released by the Great Barrier Reef Marine Park Authority showing bleached corals.
Following the 1997/1998 El Niño, the World Ocean experienced the worst case of mass coral bleaching ever historically documented. A full 16% of all coral reefs on Earth were not just bleached, but “severely” bleached1. As of today, 17 years later, we have yet to see another significant event. Students matriculating to their senior year of high school have never seen a strong El Niño wreak global havoc on issues ranging from weather, to animals natural history, to entire regional economies.
Schematic of normal versus El Niño conditions in the Pacific.
So with that in mind, we take a step back: What is El Niño? Under normal circumstances, and in simplified terms, The sun shines down on the tropical Pacific, and the tradewinds blow from east to west, piling up warm water that has absorbed all that sunlight energy high and deep, literally, around the Maritime Continent in the west2. Low atmospheric surface pressure and thunderstorms that go high into the atmosphere produce tremendous amounts of rainfall in the west, as the tradewinds have also evaporated large amounts of moisture on their journey. Once air has risen through those tall thunderstorms and arrives high in the atmosphere, and having released its moisture, moves east and sinks near South America. Dry and cool, it can now repeat the cycle of evaporating moisture and pushing warm water west. This “closed loop” is known as the Pacific Walker Circulation, named for Sir Gilbert Walker, the physicist regarded as discovering the atmospheric pressure patterns in the Pacific.
The mixed layer in the East is comparatively very thin, with cooler waters much closer to the surface, and little rainfall. Tradewinds upwell deeper, cool waters from below the thermocline: the steep temperature gradient between the upper mixed layer and cooler deeper layers. This upwelling takes place off the west coast of South America and along the equator. The Bjerknes Feedback, named for its discoverer, Norwegian meteorologist Jacob Bjerknes, follows: the cooling in the eastern tropical Pacific and equatorial central Pacific couples with and reinforces the above described Walker Circulation.… More:
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