El Niño, the seasonal Pacific Ocean warming that affects the world's weather, may not be just one little boy -- it seems to be two little boys.
Two distinct patterns of warming occur in the Pacific Ocean, according to researchers at the Georgia Institute of Technology in Atlanta, and their frequencies have been changing in recent decades.
Tracking one of these two events could yield earlier, more-accurate predictions of seasonal North Atlantic hurricanes.
The periodic warming (El Niño) and cooling (La Niña) of the eastern equatorial Pacific Ocean is known as the El Niño Southern Oscillation and affects global weather patterns.
El Niño, which occurs about every three to five years, is an ocean warming that begins in the early summer months and that reaches its peak in December.
The event can bring droughts to Australia, flooding in the Southern U.S. and Peru, changes in the Indian summer monsoon, and fewer North Atlantic hurricanes.
But after poring over more than half a century's worth of atmospheric and oceanic data collected by national and international centers, the Georgia Tech researchers concluded that there are in fact two forms of Pacific Ocean warming, and that these have different effects on the frequency and paths of North Atlantic hurricanes.
One form, eastern Pacific warming, correlates with hurricane activity identical to that of the conventional El Niño.
The other form, central Pacific warming, is associated with enhanced hurricane activity on the Eastern Seaboard of the U.S. and eastern Mexico.
"Apparently, El Niño comes in two flavors," commented Kerry Emanuel, a professor of atmospheric science at MIT who was not associated with the study. Knowing that these two independent modes have different effects could factor into predictions of Atlantic hurricanes, he added.
By tracking the second pattern, instead of just focusing on El Niño as a whole, "we may know what the character of the hurricane family in the next season will look like," said coauthor Peter Webster, professor of earth and atmospheric sciences at Georgia Tech.
North Atlantic hurricanes affect the U.S. Gulf Coast, Middle America and the Caribbean, and can cause billions of dollars in damage in the U.S. alone.
Current hurricane forecasting efforts use El Niño as a whole to predict the number and frequency of hurricanes that will occur in the summer and fall. But these predictions cannot be made before June.
