University of New Mexico, USA
Biology 576: Landscape Ecology & Macroscopic Dynamics

Predicting ENSO

Scientists have found ways to precict ENSO events by using several observed measurements. The primary measurements are the Southern Oscillation Index (SOI) and sea surface temperature (SST). Both of these measurements are calibrated to measure anomolous behavior from the norm.

Southern Oscillation Index (SOI) is the measured inverse of the oscillation in pressure between Darwin and Tahiti. Low pressure on either side of the Pacific indicates the possibility of an ENSO event. For instance, when the sea level pressure (SLP) anomaly becomes strongly negative at Tahiti, low pressure is present in the eastern Pacific. This may indicate an ENSO event in the western hemisphere. The latest SOI measures can be found by clicking here. The February, 1996, SOI indicated that the ENSO event of the past 3 out of 4 years is starting to end.

Measuring sea surface temperature in the southern Pacific Ocean (SST) is another way of predicting ENSO. Warm water anomalies moving toward the eastern Pacific indicates that an ENSO event may impact the western hemisphere. The latest measure of SST anomalies can be accessed by clicking here. The February, 1996, indicated a cooling of water temperatures in the eastern Pacific. The cooling of SST and higher pressure as measured by the SOI together indicate the arrival of a dry period for New Mexico.

Scientists have are discovering that ENSO operates in phases. Searching for a clue as to why intervals between strong ENSO events range from 2 to 7 years and average 4 to 5 years, Rasmussen et. al. (1990) have found ENSO to be paced by two clocks in the Pacific equatorial winds, one with a 2-year phase and the other with a less well defined phase of 4 to 5 years. There is an interplay between the biennial cycle and the weaker, longer period cycle. When they coincide (or in phase), a strong ENSO may result, and when they are out of phase the ENSO may be weak (Gates, David. Climate Change and its Biological Consequences Sinauer Associates, Inc. 1993. p. 244). The present pattern of SOI and SST indicate that the southwest United States will likely experience a dry period.

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Other Resources

For the latest NOAA advisory on ENSO Pacific ENSO Update

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Author:

Rich Schrader, Community and Regional Planning Graduate Student, School of Architecture and Planning. Work done in Biology Department, University of New Mexico
  • e-mail address: res13131@la.unm.edu