14th Symposium on Global Change and Climate Variations


Why did the two strongest El Niņos in the instrumental record occur in the last two decades?

De-Zheng Sun, NOAA/ERL/CDC, Boulder, CO

El Niņo warming corresponds to an eastward extension of the western Pacific warm-pool, one thus naturally wonders whether an increase in the warm-pool SST will result in stronger El Niņos. This question, though elementary, has not drawn much attention. The observation that the two strongest El Niņos in the instrumental record occurred during the last two decades when the warm-pool SST was anomalously higher, however, has added some urgency to answering this question. Here we show observational as well as model results which support a positive answer to this question. An increase in the warm-pool SST implies an enhanced heating across the equatorial Pacific. In response, stronger El Niņo develops to "pump" more heat out of the tropics and thereby regulates the warm-pool SST. Comparing the variations in the warm-pool SST with those in the global mean surface air temperature over the last 100 years suggests that the warming trend in the warm-pool SST may also have an anthropogenic origin. Preliminary analysis of climate simulations by the NCAR CCSM supports this suggestion.

Poster Session 2, Poster Session II
Tuesday, 11 February 2003, 9:45 AM-11:00 AM

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