El Niño Modoki

September 29, 2015

Most people are familiar with El Niño. During an El Niño event, trade winds that normally blow from east to west relax or even reverse direction. That allows warm water in the western Pacific to migrate eastward. The reduced upwelling of cold water from below off the coast of Ecuador and Peru that ensues wreaks havoc on the South American fishing industry. But other significant effects extend worldwide. That's what a canonical El Niño is, which as it turns out, is only one flavor.

There are others.  

Modoki is Japanese and means similar but different. In2007, a Japanese group of scientists coined the phrase when they identified the 2004-2005 El Niño event as being similar to but distinctly different from other El Niños-like the ones in 1982-1983 and 1997-1998. It was similar to previous ones in that there was anomalous warming of tropical Pacific Ocean water farther east than normal. But it was different in that the warming was not maximized over the eastern Pacific-it was more over the Central Pacific.

Other episodes of Central Pacific (CP) El Niños include 1994-1995, 2002-2003, and 2009-2010. A recent paper published in the Bulletin of the American Meteorological Society highlighted these two different flavors and their different impacts.

In the winter, Eastern Pacific (EP) El Niños in the U.S. result in warm conditions centered over the Northern Great Plains, and wet and cool conditions over the Southeastern U.S. The 1997-1998 EP El Niño likely contributed to the Great Ice Storm in Montreal, as warmer than normal conditions resulted in a freezing rain event rather than a snow event. In the summer and autumn, these EP types reduce tropical cyclone activity over the North Atlantic because they increase mid-level shear over the Caribbean (Main Development Region).

CP El Niños, on the other hand, result in much cooler and wetter conditions over the Southeastern U.S. in winter, with not much impact anywhere else. In the summer, these events can actually enhance hurricane activity over the Atlantic-with increased landfalls over the Gulf States, Mexico, and Central America. Casein point is the hurricane seasons of 2004 and 2005, which straddled a CP El Niño event.

If you are wondering which flavor El Niño is picking up this year, the lack of hurricane activity in the Atlantic and corresponding boon of activity in both the Eastern and Western Pacific basins should tell you that it's the EP flavor. Moreover,as the index continues to climb toward those that existed in1982-1983 and 1997-1998, it looks to be a full flavor as opposed to the low-calorie kind.

That will likely mean a relatively quiet end to the already quiet 2015 Atlantic hurricane season. And, it may also mean warmer than normal conditions over much of the U.S. for the coming winter.And that would definitely be a welcome relief to folks in the Northeast where places such as Boston reported record seasonal snowfall totals in 2014-2015.

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