Currently the weather is being strongly affected by an El Nino. El Nino is but one part of a weather/climate system known as the El Nino Southern Oscillation (ENSO). There are three phases of ENSO — El Nino, La Nina and neutral. ENSO is important because of its ability to change the global atmospheric circulation, which in turn, influences temperature and precipitation across the globe. The global atmospheric circulation is called the Walker Cycle and we will look at that in the next posting.
Many of you already are fully informed about the ENSO but my guess is that some of you are not. I thought it might be helpful to provide some background information. (1)
First of all, we are talking about the Pacific Ocean. The Pacific Ocean from South America to the Maritime Continent(2), a distance of about 10k miles along the equator. Usually the trade winds blow along the equator toward the west. This moves the hot surface water to the Western Pacific. The sea surface is about ½ meter higher in Indonesian than it is in Ecuador. Usually, sea-surface temperatures off South America’s west coast range from the 60°s to 70°s F, while they exceed 80°F in the “warm pool.” This description is essentially that of the neutral phase.
On occasions the easterly winds weaken and the hot water begins to flow eastward toward South America. This is the beginning of an El Nino. It typically starts in the May-June timeframe as the water flows eastward. It reaches it peak strength about December. January through March/April typically are the months that the El Nino begins to lose it strength. Some El Ninos maintain strength longer such as the 1998/1999 El Nino, which is considered one of the strongest ever.
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