Satellite imagery allows us to measure and map Pacific sea surface temperatures (SST's). The top image depicts annual average SST and shows key features of the Pacific climate system. A pool
of very warm water dominates the western Pacific, while a tongue of cool water stretches along the Equator to 160 degrees W. Cool waters prevail off the South American coast, indicating strong upwelling and high productivity. Also shown are the limits of
coral growth; as you can see, corals can only grow in areas with mean annual SST's higher than 22-23 degrees C. White circles show the locations of sites where long coral records have been analyzed and the results published.
The next two images show sea
surface temperature anomalies for the months of December through February. An anomaly is the arithmetic deviation from the mean. For example, if Shaquille O'Neal averages 30 points a game but scores 40 against the Knicks, he would have a positive
scoring anomaly of 40 minus 30, which equals 10. Likewise, if the SST anomaly in the central Pacific during a warm phase is positive 2, that means that temperatures are 2 degrees C above average. Notice the negative anomaly in the central Pacific during a
cool phase such as 1988-1989 created when strong southeasterly winds push cold surface waters away from the South American coast and into the mid-ocean. In warm modes like 1991-1992, weaker southeasterlies are unable to push as much cool water into the
central ocean. Large SST anomalies of 2 degrees C or more occur near the equator during ENSO warm mode events but the strength and location of each anomaly is different. While all ENSO events are similar, it is important to remember that no two warm events
are exactly alike; the high SST anomaly during the 1982-1983 event shifted 40 degrees further east and 5 degrees further south compared with warm events in 1986-1987 and 1991-1992.
Department of Geology and Geophysics, Rice University
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