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August 2002

El Niņo situation and prospects

Agrometeorology Group,
Environment and Natural Resources Service
FAO Research, Extension and Training Division

29 July 2002

Values of the Southern Oscillation Index, a measure of El Niņo strength based on atmospheric measurements, continued to decrease (figure 1), thereby indicating an increased likelihood of an El Niņo taking place around the end of this year.

Compared with the latest strong 1997/98 El Niņo (figure 2), the current event appears relatively weak. In fact, July 1997 values of the moving average of the Southern Oscillation Index were at -18, while average of July 2002 is about -8 only.

We mentioned in our previous updates that the atmospheric circulation patterns that are typical of El Niņo conditions had not set in; this is now happening with the trade winds weakening over the Pacific. As a result, the warm water masses located over the central Pacific (Figure 3) can move eastward and interfere with the up welling of cold water along the South-American coast. This should take place around the end of the year and constitutes one of the phenomena that, historically, was one of the earliest known manifestations of El Niņo. Note that figure 3 clearly shows the low temperatures associated with up welling of deep-ocean water along the Peruvian coast.

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