Scientists discover El Nino has a sibling

Los Angeles: El Nino, 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 Nino) and cooling (La Nina) of the eastern equatorial Pacific Ocean is known as the El Nino Southern Oscillation and affects global weather patterns.

El Nino, 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 US 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 the Georgia Tech researchers concluded there are in fact two forms of Pacific Ocean warming, and 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 Nino. The other, central Pacific warming, is associated with enhanced hurricane activity on the Eastern Seaboard of the United States and eastern Mexico.

"Apparently, El Nino comes in two flavours," said Kerry Emanuel, a professor of atmospheric science at MIT who was not associated with the study.