U.S. Dept. of Commerce / NOAA/ OAR / PMEL / Publications

Genesis and Evolution of the 1997-98 El Niño

Michael J. McPhaden

Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, Washington

Science, 283, 950–954 (1999)
Copyright ©1999 American Association for the Advancement of Science. Further electronic distribution is not allowed.

Gallery of Figures and Tables

Figure 1. Time-series sections of surface zonal wind (left), SST (middle), and outgoing longwave radiation (OLR) (right) from September 1996 to August 1998. Analyses are based on 5-day averages for between 2°N and 2°S for the TAO data, and between 2.5°N and 2.5°S for OLR. Black squares on the abscissas of the wind and SST plots indicate longitudes of data availability at the start (top) and end (bottom) of the time-series record. Positive winds are westerly, negative winds are easterly. OLR values below about 235 W m indicate an increased likelihood of deep cumulus cloudiness and heavy convective precipitation. OLR data are from the National Centers for Environmental Prediction.


Figure 2. Time versus longitude sections of anomalies in surface zonal wind (left), SST (middle), and 20°C isotherm depth (right) from September 1996 to August 1998. Analysis is based on 5-day averages between 2°N and 2°S of moored time-series data from the TAO array. Anomalies are relative to monthly climatologies that were cubic spline-fitted to 5-day intervals. The monthly SST climatology is based on data from 1950–79 (Reynolds and Smith, 1995). The monthly wind climatology is based on data from 1946–89 (Woodruff et al., 1987). The monthly 20°C isotherm depth climatology is based on subsurface temperature data primarily from 1970–91 (Kessler, 1990; Kessler and McCreary, 1993). Positive winds are westerly, and positive 20°C isotherm depths indicate a deeper thermocline. Black squares on the abscissas indicate longitudes where data were available at the start (top) and end (bottom) of the time series.


Figure 3. Monthly averaged sea-surface temperature (in degrees C) for December 1996 and December 1997. Monthly average SST anomaly for December 1997 is also shown. The anomaly is relative to the SST climatology referred to in Fig. 2.


Figure 4. SST anomalies for the region from 5°N to 5°S, 90°W to 150°W from a combination of shipboard data through 1991 and analysis of blended satellite/in situ data afterward. The shipboard data are described in (Kaplan et al., 1998) and the blended product is described in (Reynolds and Smith, 1994). Warm anomalies (in red) greater than about 0.5°C generally indicate El Niño events. Cold anomalies (in blue) less than about -0.5°C generally indicate La Niña events.


Figure 5. Five-day averaged time series of surface zonal winds and SST from a mooring station on the equator at 125°W. The normal seasonal cycle is shown by magenta lines.


Figure 6. Observed heat content anomalies (from 0 to 400 m depth) averaged between 2°N and 2°S from the TAO array. Temporal resolution is 5 days and contour interval is 0.1 × 10 J m. Heat content anomalies are relative to the subsurface temperature climatology referred to in Fig. 2.


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