Bookmark and Share Email this page Email Print this page Print Feed Feed

Major El Nino event brewing?

Apr 18, 2014
This time-longitude plot tracks the history of westerly wind events, and where they have occurred along the equator. A strong westerly wind burst began roughly two weeks ago in the western equatorial Pacific.

This time-longitude plot tracks the history of westerly wind events, and where they have occurred along the equator. A strong westerly wind burst began roughly two weeks ago in the western equatorial Pacific.

Kim Cobb's Lab, Georgia Tech

The El Nino (or El Nino/Southern Oscillation, ENSO) climate event in the eastern Pacific can have widespread weather effects in the Western Hemisphere, changing the patterns of storms, bringing drought to some areas or high rainfall to others. And for ocean voyagers, unsettled weather may be more intense than normal or shift from its usual location. The last big El Nino events were in 1997-98, 1982-83 and 1972-73. According to researchers we are about due for another large-scale El Nino.

Some of the signs are there. As Paleoeclimate researcher Kim Cobb from Georgia Tech writes in her blog:

"While considerable uncertainty surrounds the conception of an El Niño event, most scientists agree that it helps to have the following features in place:

"1) An ocean that is primed for an event (enough time elapsed since the last major event). The last Big One was the 1997-1998 El Niño, and before that was the 1982-1983 El Niño, and before that the 1972-1973 El Niño. By this simple metric, we are due for a Big One. Given that the last moderate El Niño event was 2009-2010, we are at least due for One. Some El Niño scientists describe the pacemaker for the El Niño-Southern Oscillation events as a "recharge oscillator", whereby heat accumulates in the western Pacific ocean until it is discharged to the atmosphere by a cascade of positive feedbacks triggered by . . . (see #2 below).

"2) A strong burst of westerly winds along the equator in the west Pacific. Usually, trade winds blow steadily from the east to the west ('easterly' winds) across the tropical Pacific, and they maintain the temperature structure of the equatorial Pacific:  cool waters in the East, and warm waters in the West. Essentially, the trade winds keep the 'thermocline' (the boundary between warm surface waters and the cool deeper waters) close to the surface in the eastern Pacific. When a burst of westerly winds occurs in the western Pacific, it triggers a 'downwelling wave' that propagates eastward along the equatorial thermocline. When it reaches the eastern Pacific, it pushes the thermocline to deeper depths, leading to warmer sea-surface temperatures in this region roughly 2 months after the westerly wind burst. [For more information on ENSO physics, see this recent and exhaustive review by some ENSO heavy-hitters, in press in "Coral Reefs of the Eastern Pacific" (Springer).]

"At a certain point (and this is where the mystery comes in), the warming in the central to eastern Pacific is strong enough to undermine the strength of the trade winds themselves. The thermocline further deepens in the east, and surface ocean temperatures warm even more. At that point, the system is moving inevitably towards an El Niño event that will reach its maturity sometime between November and February - a well-choreographed and now-familiar dance between the tropical Pacific atmosphere and ocean."

But the NOAA's Climate Prediction Center is predicting a 50% probability of a major El Nino event occurring this year (although chances may rise as the summer progresses): "While ENSO-neutral is favored for Northern Hemisphere spring, the chances of El Niño increase during the remainder of the year, exceeding 50% by summer."

Add your comment: