El Nino, the Not-so-fair Weather Friend, Is Back

WASHINGTON (Agencies via Xinhua) A massive pool of warm ocean water is causing changes in the atmosphere that could produce unusual weather around the world in the next few months, the US National Weather Service reported on Monday. 

As a result of this phenomenon, known as El Nino，more rainfall than normal is likely this winter across some areas of the United States, with unusually warm or cold weather in other parts of the country.

Currently the phenomenon is marked by a warm pool of water along the equator extending from the international dateline nearly to the coast of South America. That water is nearly 4 degrees Fahrenheit above normal, explained Vernon Kousky of the climate centre.

This warm water“spreads almost a quarter of the way around the globe. So it's massive and it has an impact on our weather. It has a global influence …because it disturbs the atmospheren", said Dave Rodenhuis, director of the climate centre.

Ei Nino is“probably the most important climate event beyond the annual cycle of seasons”，he added.

Because the changes tended to be first noticed around Christmas, the phenomenon was given the name El Nino, which is Spanish for child, a term often used to refer to the baby Jesus.

The phenomenon occurs every three to five years, sometimes in a mild form and sometimes strongly affecting weather patterns worldwide. Details of its causes are not fully understood, but when it occurs，unusually warm air can be pumped into Canada, Alaska and the northern United States. At the same time，conditions tend to be wetter than normal along the US Southeast Coast and the Gulf of Mexico. And the Atlantic and Caribbean hurricane season tends to be milder than usual.

The strong El Nino of 1982〜1983 was blamed for worsening the devastating drought in Africa, causing a series of severe winter storms to come ashore in California, spawning the first typhoon to strike French Polynesia in 75 years— followed by five more in five months—deluging Peru and Ecuador with torrential rains and promoting the worst drought in two centuries in Australia.

Overall damage was estimated at between $2 billion and $8 billion by a United Nations analysis and the death toll topped 1500 worldwide.

That doesn't mean that the disruption will be as great this time, however. A mild El Nino in 1986〜1987 was barely noticed, for example.

Another weather phenomenon is an Enso, the warming of the water in the central and eastern Pacific accompanied by changes in air pressure and winds over the ocean.

The normal easterly winds that push warm water toward Asia diminish or are replaced by westerlies, and the warm water sloshes back toward the Americas.

Kousky said the current Enso seems moderate, with characteristics in between the events of 1982〜1983 and 1986〜1987. “But we can't rule out further intensification of this event”, he warned.

The fact that warm water is more likely to evaporate than cooler water means it has more warm, humid air above it. Warm air is buoyant, tending to rise and cause its moisture to condense into clouds. That results in more rainfall in the warm area, he said.

The effects are spread out by the jet stream, a high altitude river of fast-moving air going west to east, that guides weather across the world and often forms the boundary between cold polar and warmer air to the south.